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Mirror lens not good for Moon shot?
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PostPosted: Sun Mar 20, 2011 5:10 am    Post subject: Reply with quote
Moon shot, when it was at its closest (I wish it were closer)...Hand held should have used a tripod as it was windy.
This one I used the sharpening tool in windows live gallery.






Last edited by mo on Sun Mar 20, 2011 6:26 am; edited 1 time in total


PostPosted: Sun Mar 20, 2011 6:01 am    Post subject: Re: Mirror lens prices insane? Reply with quote
cooltouch wrote:

Something that I just don't understand is this: Samyang has proven that they can build outstanding optics when they want to. So why don't they build to this same quality level with mirror lenses too?


The 500/6.3 seems to be quite good. The 500/8 model is a dud.


PostPosted: Sun Mar 20, 2011 7:09 am    Post subject: Reply with quote
Looks like I am addicted to shooting moon. Here we go tonight, the biggest/brightest moon, still Beroflex 500mm f8. Also I found moon shot can actually be served as a good test method for telephoto lens. I tried 200mm, 300mm and some zoom 80-200mm, 70-210mm. I found the moon photo quality is good for testing both resolution and infinity focus check.



PostPosted: Sun Mar 20, 2011 7:12 am    Post subject: Reply with quote
Shocked Damn that is good!


PostPosted: Sun Mar 20, 2011 7:32 am    Post subject: Reply with quote
Nice..! What's with the green fringing, though?

Mirror lenses, "in theory" should be good for solar system objects, like planets and the moon, since mirrors do not produce chromatic abberations, unlike glass. That's why (among other things) Schmidt-Cassegrain scopes (pretty much the same thing as "mirror-lenses" in design) are preferred for planetary astrophotography.

Of course, with the moon, a nice APO scope works well, though you need to figure out some way to magnify it more; my Megrez 90 is only 558mm in focal length, so a bit too short even for the moon:


Super Moon by Dr. RawheaD, on Flickr


I would've shot it with my Celestron C-8 (1200mm) if I had the will power to carry my 60 pound setup down the stairs today (I didn't Smile )


PostPosted: Sun Mar 20, 2011 9:23 am    Post subject: Reply with quote
A couple of shots I just took this night.

With Tokina 500/8:


http://www.flickr.com/photos/laurentiucristofor/5541941097/

With Vivitar Series 1 800/11, solid cat:


http://www.flickr.com/photos/laurentiucristofor/5542521428/

Both at ISO 800 on tripod.


PostPosted: Sun Mar 20, 2011 10:43 am    Post subject: Reply with quote
This is my try: not good Sad

Tamron SP 500mm F/8 55B plus duplicator Tamron 01F, on the Lumix GF1:



With the 2x factor of the GF1 and the duplicator, it gives 2.000mm.

Taking out the multiplier 01F:



Still not good.
Regards.

Jes.


PostPosted: Sun Mar 20, 2011 11:34 am    Post subject: Reply with quote
Jes, I don't think these are bad at all. Some sharpening and contrast adjustment would do wonders.


PostPosted: Sun Mar 20, 2011 4:22 pm    Post subject: Reply with quote
I didn't even bother again with my Tamron 500. I still prefer my old Century Precision Optics 500mm f/5.6.

ISO 100, 1/125 @ f/11


The mirror vs. refractor debate is an old one in astronomy. Mirrors are superior to refractors in their sheer ability to gather light. Refractors are superior to mirrors in their resolution capabilities. So what this means is you need a pretty big mirror to equal a relatively small refractor in terms of resolution. For this comparison, astronomers discuss objective (front element) diameter, rather than focal length, because it is this that determines the amount of light that can be gathered. But I would say roughly that at least an 8" mirror is needed to equal the resolution of a 4" refractor. Rawhead's 60-lb Celestron C8 is an 8" mirror and it probably delivers performance equal to a decent 4" APO refractor. However, it gathers 4x as much light as a 4" will. For planetary astronomy, refractors work rather well because planets are generally fairly bright objects. For celestial astronomy, however, the mirrors excel because of their superior light-gathering ability with regard to dim or very distant objects.

Here's a photo I took of Jupiter and its Galilean moons a few months ago with my CPO 650mm f/6.8. Slight upsized from 100% and Photoshop was used to bump up the brightness of one of the moons. That old CPO 650 has a 3.75" front element diameter. It would probably take about an 8" mirror to equal this shot. Although some of the new techniques, like "stacking" could very well prove me wrong. But I'm referring to more traditional, old-school methods.



PostPosted: Sun Mar 20, 2011 5:36 pm    Post subject: Reply with quote
Your Jupiter shot is very impressive.


PostPosted: Sun Mar 20, 2011 8:49 pm    Post subject: Reply with quote
I worked a bit on the Vivitar shot, to increase contrast. Here's the result:


http://www.flickr.com/photos/laurentiucristofor/5544315378/

The Beroflex and Century Precision Optics shots are excellent.


PostPosted: Sun Mar 20, 2011 10:35 pm    Post subject: Reply with quote
Thanks, Laurentiu -- I'm fond of my old Century. I think that if you were to bump up the sharpness slightly on your Vivitar's image, you could improve it even more.


PostPosted: Sun Mar 20, 2011 11:18 pm    Post subject: Reply with quote
Not a mirror lens, but the fabulous-nonetheless Tamron Nestar 400/6.9 coupled with a Canon 1.4x TC and Sony Nex-5 Smile

Lots of shadow/highlights and sharpening applied Laughing


Moon by ManualFocus-G, on Flickr


PostPosted: Mon Mar 21, 2011 6:46 am    Post subject: Reply with quote
cooltouch wrote:
I think that if you were to bump up the sharpness slightly on your Vivitar's image, you could improve it even more.


Thanks for the encouragement. How about this version?


http://www.flickr.com/photos/laurentiucristofor/5545544531/


PostPosted: Mon Mar 21, 2011 7:36 am    Post subject: Reply with quote
This is my Makinon 500/8, yesterday night (PP applied). I was glad, but having looked through this thread, now no more Smile . I tried also to duplicate my Takumar 200, but I discovered it does not go to infinity, missing a little bit. I will try with some other adapter.

[/img]


PostPosted: Mon Mar 21, 2011 1:01 pm    Post subject: Reply with quote
rawhead wrote:
Mirror lenses, "in theory" should be good for solar system objects, like planets and the moon, since mirrors do not produce chromatic abberations, unlike glass. That's why (among other things) Schmidt-Cassegrain scopes (pretty much the same thing as "mirror-lenses" in design) are preferred for planetary astrophotography.


I have read the opposite (from a telescope/binoculars manufacterer). They wrote that refractors are preferred over reflectors for planets, because of their higher contrast (which makes patterns and colors of the planets more visible). Reflectors have lower contrast because of the central obstruction by the secondary mirror. They can have larger apertures though and their resultant higher light gathering capacity makes them better suitable for things like nebulae (faint sky objects).

I'm no expert though, but the above makes sense to me. Smile

Edit: I essentially repeated what Cooltouch wrote... being too hasty to reply again.

@Cooltouch: what's it like to see Jupiter through the eyepiece of that telescope? Better or worse than what you see in your picture?


PostPosted: Mon Mar 21, 2011 1:12 pm    Post subject: Reply with quote
Some amazing results on this thread, especially the Jupiter shot. It's hard to believe that such good results can be obtained with short focal lengths, like 500mm.

I never really got the hang of high-resolution lunar/planetary imaging, so I switched to shooting DSOs, which are often large and faint, and don't usually need high resolution imaging.


PostPosted: Mon Mar 21, 2011 1:20 pm    Post subject: Reply with quote
Quote:
I have read the opposite (from a telescope/binoculars manufacterer). They wrote that refractors are preferred over reflectors for planets, because of their higher contrast (which makes patterns and colors of the planets more visible).


I think the contrast issue mostly affects visual observing. I think the best planetary imagers use fairly large SCT (reflector scopes) and do very careful collimation before each shot to get the best possible image quality at the center. They also use video cameras (webcams, security cams, etc.).

For DSO imaging of small DSOs, like planetary nebulae and galaxies, the best imagers often use RC (Richey-Chretien) mirror scopes, which have a huge central obstruction, but good image quality across the whole field.


PostPosted: Mon Mar 21, 2011 4:28 pm    Post subject: Reply with quote
AhamB wrote:

@Cooltouch: what's it like to see Jupiter through the eyepiece of that telescope? Better or worse than what you see in your picture?


It was essentially the same, really. I could see the banding and the colors of Jupiter, and all four Galilean moons were visible, although the most distant one was rather faint. So in post processing I brought up the illumination of that faint moon a bit so it would be more easily visible.

Now, this wasn't a telescope, though. This was my old Century Precision Optics 650mm f/6.8 -- a T-mount lens that was built back in the 1970s I'm guessing. So I was observing Jupiter and the moons on my camera's LCD screen, using Live View, and also through the viewfinder.

Here's the CPO 650 with my Pentax KX mounted on it:


PostPosted: Mon Mar 21, 2011 4:37 pm    Post subject: Reply with quote
s58y wrote:
Quote:
I have read the opposite (from a telescope/binoculars manufacterer). They wrote that refractors are preferred over reflectors for planets, because of their higher contrast (which makes patterns and colors of the planets more visible).


I think the contrast issue mostly affects visual observing. I think the best planetary imagers use fairly large SCT (reflector scopes) and do very careful collimation before each shot to get the best possible image quality at the center. They also use video cameras (webcams, security cams, etc.).

For DSO imaging of small DSOs, like planetary nebulae and galaxies, the best imagers often use RC (Richey-Chretien) mirror scopes, which have a huge central obstruction, but good image quality across the whole field.


All this is generally true, but it is because "fairly large" mirror telescopes are much larger in objective diameter than refractors. A 6" reflector is considered small, and is relatively cheap. A 6" refractor is huge and extremely expensive. Refractors have another drawback besides CA problems -- they can get only so large before the sheer weight of the optic begins to distort the image. Reflectors don't have this problem since a mirror can be supported from the underside. This is why the largest telescopes are all mirrors. The very biggest refractors were built around the turn of the 20th century -- they had reached their structural limits by then.

But there has always been the crowd who prefers the seeing with a good refractor -- say a 4" APO. For amateur planetary astronomy, it's really hard to beat. Granted for DSOs (Deep Sky Objects), it gives a lot away to reflectors. But I wouldn't be surprised to hear a refractor enthusiast respond that it just takes a bit longer exposure to get the same results.


PostPosted: Mon Mar 21, 2011 5:18 pm    Post subject: Reply with quote
martyn_bannister wrote:
Jes, I don't think these are bad at all. Some sharpening and contrast adjustment would do wonders.


Thanks for your comment, Martin.
The second one has contrast and strong sharpening Sad
I'll give them another try.

Regards.
Jes.


PostPosted: Mon Mar 21, 2011 7:08 pm    Post subject: Reply with quote
I have seen some very good terrestrial (bird) shots made with APO refractors, btw -- something that is simply not possible with reflectors (due to the poor bokeh).


PostPosted: Mon Mar 21, 2011 7:32 pm    Post subject: Reply with quote
Jesito wrote:

The second one has contrast and strong sharpening Sad
I'll give them another try.


Post processing seems to be half of the work needed for these shots. The 500 with 2x TC should give you a pretty large image to work with - I'd start with that.

AhamB wrote:
I have seen some very good terrestrial (bird) shots made with APO refractors, btw -- something that is simply not possible with reflectors (due to the poor bokeh).


Of course it's possible. Donut bokeh doesn't form out of nowhere - it all depends on the background.


PostPosted: Mon Mar 21, 2011 7:59 pm    Post subject: Reply with quote
When I compared reflectors to refractors, I was comparing dollar for dollar. If you can spend top-dollar for a big, true apochromatic refractor, they are hard to beat for anything but capturing the faintest deep sky objects.

However, If you compare a $500 reflector to a $500 refractor, the $500 reflector is going to give you better results for planetary astrophogtography because of the lack of chromatic aberration. You don't want color fringing around your already pretty small image of the planet Smile

If you want to check out some truly amazing planetary astrophotography using fairly lowly equipments (Meade Starfinder 10 + webcam), check this guy out:

http://www.astrokraai.nl/viewimages.php?category=3


PostPosted: Mon Mar 21, 2011 11:22 pm    Post subject: Reply with quote
Took this one a couple of days prior to the SuperMoon. Used my Tamron 500mm F8 mirror. Heavily cropped from my K7. I think it turned out good.
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