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Lens equivalence question...
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PostPosted: Wed Jun 26, 2019 6:50 am    Post subject: Lens equivalence question... Reply with quote

OK so I've managed (a while ago admittedly) to get a Pentacon Six mount CZJ Flektogon f/4 50mm lens stuck on an EOS adapter.


Given that it's now effectively an EOS lens (it is that stuck) what would be its equivalent focal length on an EOS 5DSr? Would I get anywhere near MF quality given its full-frame at 50MP?

Help a luddite out.. 😆

I'm asking ad I was figuring to try out my m42 flektogon 20/4 at the weekend for some architectural/landscape style work (weather permitting) and was wondering if it would be worth lugging the 50/4 to compare the two...


PostPosted: Wed Jun 26, 2019 7:14 am    Post subject: Reply with quote

It's a 50mm lens, so unless your adaptor has some "turbo-booster" optics in it, it remains a 50mm lens and will perform as a "standard" lens in full-frame format.

The comparison between the two Flektogons may be interesting, but take along a modern lens of similar focal length(s) if you have one, then you'll have a real idea of the benefits and pitfalls of using older glass on a modern body.

Good luck ... it'll be interesting to see the results Wink


PostPosted: Wed Jun 26, 2019 7:32 am    Post subject: Reply with quote

^^^ Correct.

Millimeters are millimeters and relative opening is relative to those millimeters, not sensor size.
It will work on FF sensor exactly the same as native FF 50mm F4 would (if there ever was one).


PostPosted: Wed Jun 26, 2019 9:24 am    Post subject: Reply with quote

If you want to calculate equivalence to to Pentacon six system, you would need a 92mm lens to get the same FOV you get on the canon


PostPosted: Wed Jun 26, 2019 10:56 am    Post subject: Reply with quote

Deleted.

Last edited by Sciolist on Wed Jun 26, 2019 6:17 pm; edited 1 time in total


PostPosted: Wed Jun 26, 2019 11:21 am    Post subject: Reply with quote

My favorit explanation to this question is to forget what system the lens was made for. Think instead of what system it is adapted to. It is a 50mm f/4 just like my Macro Takumar 50mm f/4, but with much larger image circle.



Now if you you could use more of that image circle, like a on Pentacon 6 it will be a wide angle. Or if there was a speed booster adapter like kypfer said.


I found a very cheap Pentax 67 55mm f/3.5 that I couldn't resist. When testing it I was surprised at finding it wasn't excellently sharp across the field on my full frame Sony a7.
Please post some shots with the Flektogon after the test!


Last edited by blotafton on Wed Jun 26, 2019 11:31 am; edited 1 time in total


PostPosted: Wed Jun 26, 2019 11:26 am    Post subject: Reply with quote

Hmmm.....................
Place your camera on a tripod facing a fixed subject.
If you put a 50mm DX lens @f4 on your Canon and take an image, then replace that lens with a full frame 50mm lens @f4 and take the same image, then replace that with a 50mm lens from medium format @f4 and take the same image again......... guess what will change ................
Nothing.
You will have three near identical images.
Your sensor doesn't change size, so the result is the same.
Happy snaps
Tom


PostPosted: Wed Jun 26, 2019 11:35 am    Post subject: Reply with quote

Oldhand wrote:
Hmmm.....................
Place your camera on a tripod facing a fixed subject.
If you put a 50mm DX lens @f4 on your Canon and take an image, then replace that lens with a full frame 50mm lens @f4 and take the same image, then replace that with a 50mm lens from medium format @f4 and take the same image again......... guess what will change ................
Nothing.
You will have three near identical images.
Your sensor doesn't change size, so the result is the same.
Happy snaps
Tom



Fair point. What happens in reality. If anyone can carry out Oldhand's test, or has done something similar in the past, it would be most appreciated. I'm at odds here with Oldhand, but very happy to be corrected as I have not carried out this real world test myself.


PostPosted: Wed Jun 26, 2019 11:41 am    Post subject: Reply with quote

Sciolist wrote:
Oldhand wrote:
Hmmm.....................
Place your camera on a tripod facing a fixed subject.
If you put a 50mm DX lens @f4 on your Canon and take an image, then replace that lens with a full frame 50mm lens @f4 and take the same image, then replace that with a 50mm lens from medium format @f4 and take the same image again......... guess what will change ................
Nothing.
You will have three near identical images.
Your sensor doesn't change size, so the result is the same.
Happy snaps
Tom



Fair point. What happens in reality. If anyone can carry out Oldhand's test, or has done something similar in the past, it would be most appreciated. I'm at odds here with Oldhand, but very happy to be corrected as I have not carried out this real world test myself.

In reality it happens exactly as I have described.
I did this test some time back and the results were the same.
Don't get hung up on what the lens image circle can deliver for its particular format.
If the sensor that you are using stays the same size, then it will always "see" the same part of the image from the same focal length.
The rest of what the lens "sees" is too wide to be recorded
Tom


PostPosted: Wed Jun 26, 2019 12:23 pm    Post subject: Reply with quote

Sciolist wrote:
Oldhand wrote:
Hmmm.....................
Place your camera on a tripod facing a fixed subject.
If you put a 50mm DX lens @f4 on your Canon and take an image, then replace that lens with a full frame 50mm lens @f4 and take the same image, then replace that with a 50mm lens from medium format @f4 and take the same image again......... guess what will change ................
Nothing.
You will have three near identical images.
Your sensor doesn't change size, so the result is the same.
Happy snaps
Tom



Fair point. What happens in reality. If anyone can carry out Oldhand's test, or has done something similar in the past, it would be most appreciated. I'm at odds here with Oldhand, but very happy to be corrected as I have not carried out this real world test myself.


Well, I don't have a medium-format 50mm, but I've done comparison tests between lenses taken from medium-format folding cameras, 6x6cm & 6x9cm, and lenses of similar focal length that I do have from my 35mm film days and ... lo-and-behold ... there's no significant image size difference between lenses of similar focal length when used on the same camera body!

The image quality or characteristics (colour rendition, bokeh etc.) might be noticeable, which is what I was looking for, but a 1938-vintage 10.5cm Trioplan from a 6x9 folder has similar image size and perspective characteristics as a Fujinon 100mm from the 1980's or a Tamron zoom of much more recent vintage when set to similar focal length Wink


PostPosted: Wed Jun 26, 2019 3:18 pm    Post subject: Reply with quote

Sciolist wrote:
Your 50mm medium format will provide a FOV equivalent to a 35mm on full frame

No, it would not.


PostPosted: Wed Jun 26, 2019 3:36 pm    Post subject: Reply with quote

If you could get the adapter off the image circle is large enough it could be used with perspective control..... (tilt/shift)


PostPosted: Wed Jun 26, 2019 3:53 pm    Post subject: Reply with quote

Sciolist wrote:
^^D1N0 has touched on the pertinent question - the Field of View (FOV).

Your 50mm medium format will provide a FOV equivalent to a 35mm on full frame. Everything else will appear as 50mm, e.g perspective etc..


I read this lens is meant to be a bit of a looker. Congrats on snagging one Gott Like 1 .


In terms of quality of image, there are some comments here -

http://www.mflenses.com/flektogon-50mm-f4-mc-lens-review.html


Embarassed

The mistake I have also made is confusing the reference. The crop factor refers to 35mm FF. Referring to medium format the 50mm lens gives the same angle of view as 35mm lens on 35mm FF camera. However referring to 35mm FF any 50mm lens from any format gives the same angle of view as a 50mm lens made for 35mm format.


PostPosted: Wed Jun 26, 2019 6:16 pm    Post subject: Reply with quote

Oldhand wrote:

In reality it happens exactly as I have described.
I did this test some time back and the results were the same.
Don't get hung up on what the lens image circle can deliver for its particular format.
If the sensor that you are using stays the same size, then it will always "see" the same part of the image from the same focal length.
The rest of what the lens "sees" is too wide to be recorded
Tom



My question was rhetorical, not direct, hence the lack of a question mark.


But thanks for clarifying what happens. That's what I was looking for. I'll delete my post and stop muddying the waters.


PostPosted: Wed Jun 26, 2019 10:28 pm    Post subject: Reply with quote

If you compare 2 50mm lenses properly focused on a scene, if you look throught the lens they should frame a view the same way. There are however lots of lenses that are near but not exactly the focal length printed on the lens so you may find a slight missmatch.


PostPosted: Thu Jun 27, 2019 12:34 am    Post subject: Reply with quote

I had some time this morning so I took these images to make it clearer to see.
The four lenses were all shot on APSc sensors at f4
There are minor variations of course as Slalom has said, but they are essentially the same image.
The lenses are:
Sigma 17-70 shot at 55mm (on Nikon D300 as this was the only 55mm DX lens that I had)
Canon FL 55mm - Full frame lens shot on Fujifilm X-E2s
Mamiya 645 55mm - Small medium format shot on Fujifilm X-E2s
SMC Pentax 67 55mm - larger medium format shot on Fujifilm X-E2s

Here are the images - nothing special, but I included the post as a frame of reference


#1 Sigma 17-70 shot at 55mm


#2 Canon FL 55mm - Full frame lens


#3 Mamiya 645 55mm - Small medium format


#4 SMC Pentax 67 55mm - larger medium format


Hope this helps
Tom


Last edited by Oldhand on Thu Jun 27, 2019 1:24 am; edited 1 time in total


PostPosted: Thu Jun 27, 2019 1:11 am    Post subject: Reply with quote

Like 1 Like 1 Bravo! Well done test imho. See the dof is identical as well as framing!


PostPosted: Thu Jun 27, 2019 6:10 am    Post subject: Reply with quote

Nice Like 1 .


PostPosted: Thu Jun 27, 2019 7:01 am    Post subject: Reply with quote

Oldhand wrote:
I had some time this morning so I took these images to make it clearer to see.
The four lenses were all shot on APSc sensors at f4
There are minor variations of course as Slalom has said, but they are essentially the same image.
The lenses are:
Sigma 17-70 shot at 55mm (on Nikon D300 as this was the only 55mm DX lens that I had)
Canon FL 55mm - Full frame lens shot on Fujifilm X-E2s
Mamiya 645 55mm - Small medium format shot on Fujifilm X-E2s
SMC Pentax 67 55mm - larger medium format shot on Fujifilm X-E2s
Hope this helps
Tom


Excellent examples!


PostPosted: Thu Jun 27, 2019 11:55 pm    Post subject: Reply with quote

Thank you for the appreciation.
One thing to notice is that the Pentax 67 lens has less definition/clarity because the sensor is picking up only a very small portion of the image circle.
Here is a graphic from:
https://www.filnenna.com/blog/2017/6/6/is-digital-medium-format-full-frame

to show the comparison
Tom


#1


PostPosted: Fri Jun 28, 2019 6:26 am    Post subject: Reply with quote

Finally got round to reading all of this - I've started a new job so busy doesn't even begin to describe it! 😭

First of all, thanks for all your input, it's very appreciated.

I figure my confusion has been a combination of 35/mf lens equivalence and the lens image circle, which as oldhand said is limited by the sensor size.

And thanks Sciolist, the worst of it being that the lens I got stuck is a more modern MC version while the replacement I got for it is an older zebra version with a temperamental aperture..

The weather is looking good this weekend so I'll give it a try on my 5DSr. Though not the same focal length I'm figuring I'll also use my m42 Flektogon 20mm f/4 to see what the resolution is like in comparison. What I was wondering is that give the sensor is 50MP compared to say the average 26MP or so of a full frame how much detail this will allow the camera to capture with the MF lens..

Only one way to find out I suppose... 😆

Plus at the end of the day, I suppose I've got one of the most ridiculous looking 50mms for my DSLR.. 😂

As for comparing it with a modern lens, I'm going to be limited to an EF 24-70 L since I've traded in all my other modern glass to feed my MF habit.. 😨


PostPosted: Fri Jun 28, 2019 7:04 am    Post subject: Reply with quote

[quote="Gott23] ...since I've traded in all my other modern glass to feed my MF habit.. 😨[/quote]


We are not worthy sir Like 1 . Have fun.


PostPosted: Fri Jun 28, 2019 7:10 am    Post subject: Reply with quote

Sciolist wrote:
[quote="Gott23] ...since I've traded in all my other modern glass to feed my MF habit.. 😨



We are not worthy sir Like 1 . Have fun.[/quote]

😂😭

Thanks!

Yeah I've had a few people think I'm mad but I explain it in terms of painting in having more brushes gives more different results. And with what I've used so far I'm more than happy as the analog feel produced by them is something quite hard to capture fully digitally. I only really kept the 24-70 as its a proper workhorse/jack-of-all-trades..

Hopefully once I've settled a bit more (also relocated to other end of the country recently) I can start to focus on fully analog as well.. (hence why a Lab-Box is top of my Christmas list! 😆)


PostPosted: Sat Jun 29, 2019 10:14 am    Post subject: Reply with quote

Sciolist wrote:
Oldhand wrote:
Hmmm.....................
Place your camera on a tripod facing a fixed subject.
If you put a 50mm DX lens @f4 on your Canon and take an image, then replace that lens with a full frame 50mm lens @f4 and take the same image, then replace that with a 50mm lens from medium format @f4 and take the same image again......... guess what will change ................
Nothing.
You will have three near identical images.
Your sensor doesn't change size, so the result is the same.
Happy snaps
Tom



Fair point. What happens in reality. If anyone can carry out Oldhand's test, or has done something similar in the past, it would be most appreciated. I'm at odds here with Oldhand, but very happy to be corrected as I have not carried out this real world test myself.


OH is 100% correct, the focal length and the sensor dimensions dictate the angle of view, any 50mm lens that covers the frame will look the same(framing).

A smaller sensor crops the image projected from the lens, the lens doesn't know or care what size sensor is being used.

A larger sensor will have more angle of view from that same lens, till the sensor becomes larger than the projected image circle, then vignetting will occur. The same thing happens with smaller format lenses on a FF sensor.

A 16mm movie lens and a large format lens with the same focal length will - within the overlapping area of their image circles - have the exact same field of view. Keep in mind that many lenses are not exactly the focal length that's printed on the ID ring, a "50mm" may actually be 52mm.

Unfortunately there is lots of misleading information out there, starting with how people describe crop factor, "a 50mm lens becomes 75mm lens", like changing the sensor magically alters the physics working within the lens to change its focal length, My preferred way to state it is: "A 50mm lens on APS-C will have the same AOV/FOV of a 75mm lens on FF" (80mm on Canon APS-C)


Last edited by Lightshow on Sat Jun 29, 2019 10:34 am; edited 1 time in total


PostPosted: Sat Jun 29, 2019 10:20 am    Post subject: Reply with quote

Lightshow wrote:

OH is 100% correct, ...



I couldn't agree more Lightshow.

Who is this Sciolist guy?