Astrophotography recommendations

luigis · Joined: 27 Aug 2009 Posts: 22

Hi Guys,

Any recommendations about MF lenses that are very good for astrophotography?
Sharpness wide open, absence of comma, etc are important things.

I appreciate all your suggestions!

Luis

cheekygeek · Joined: 05 Aug 2008 Posts: 183

What mount, Luis?

Also, are you interested in wide-field astrophotography or more telephoto work? Are you talking about short exposure (unguided) or longer-exposure guided astrophotography?

Are you using a digital camera or film? If digital, what is your focal length multiplier?

Scheimpflug · Expire: 2011-11-18

I don't have a lot of Astrophotography experience, but I can add a few more criteria for you:
* Accurate infinity stop and/or ability to adjust it
* Not susceptible to focus creep or zoom creep when pointed upwards

cheekygeek · Joined: 05 Aug 2008 Posts: 183

Yes, I would not recommend zooms for anything much more than short exposure moon shots.

If you are shooting with a crop digital camera coma may be less of a concern, since it is normally an edge-of-field/corners problem and you are cropping those out with your focal length multiplier.

If we are talking m42 lenses here, I think you would be happy with fast Takumars: 35mm f2, 50mm f1.4, and 85mm f1.8/1.9 - although only the 50mm f1.4 is still very reasonably priced.

I have an old Vivitar 28mm f2 that is stuck wide open (Canon FD mount). I bought an old TX to use simply for meteor showers with it.

AhamB · Joined: 22 Jun 2008 Posts: 733 Location: Germany

The Contax Planar 1.7/50 should be very good for astro.

luigis · Joined: 27 Aug 2009 Posts: 22

JWH · Joined: 26 Aug 2009 Posts: 120 Location: Netherlands

For proper Astrography you want atleast a 200mm, that's already widefield. Lower mm's will give it a wider field but will also make details in galaxies, nebulae or clusters too small to properly see any details in them. If you take M31, Andromeda, for example. It is already frame-filling with 400mm.

You'd also want to look like a lens that is relatively sharp from corner to corner and doesn't show much distortion. This often occurs at low f-stop lenses such as the 135/1.8-series or Takumar 50/1.4.

I've tried astrography myself with a Carl Zeiss 200/2.8 MC and I was very pleased with the result. The result is added below which is at original size. A stack from 40x30s exposures and 20x30s darks. The guiding was far from perfect so the stars are a bit mishaped.

M13 Widefield ORIGINAL SIZE

symphonic · Joined: 23 May 2010 Posts: 550 Location: SE Europe, Croatia

@JWH That's very nice! How did you do the guiding, with a barn-door tracker or a telescope mount?

M13 is a bit to small for shooting on a 200mm, now that the summer is here, the area around Saggitarius would be a great target Very Happy

pat donnelly · Posted: Wed Jun 30, 2010 11:27 am Post subject:

Forgive me for going so far off topic, but do astrophotographers ever use polarizing filters?

I ask because of a theory of mine which is probably already in practice?

Does the following make sense?

When out at night moonlight casts a wonderful spell. In addition to reflecting the light of the nearby star, it polarizes the light. Viewed through polarizing plastic, whether or not contained in high quality glass, the light will dim and slowly disappear as the linear filter is rotated until nearly all the light is gone!

Whatever the source of the light from a star it is clearly not polarized. When an object reflects the light, it is polarized and thus we receive a tiny amount upon earth. By employing suitable means and a polarizing filter it should be possible to leave an image on a "computer screen" that shows many faint objects that are not self illuminating, but reflect polarized light only.

Taking a "shot" of the night sky will virtually fill the image with light. Taking another, longer one, to account for the roughly one quarter reduction in light caused by the filter, will show all the self illuminating objects less those that reflect. It may need two or three such shots, taken with a one third rotation of the polarizing filter, to eliminate all the reflecting objects. Taking a negative of the first shot and combining it with each of the others will eliminate all the self illuminating objects. What is left is asteroidal with the occasional plotted and named object among them. Repetition of this over time will enable plotting and ascertain the degree of likely proximity to be expected over the near future.

visualopsins · Expire: 2025-04-11

Imo, astrophotography is the most brutal of lens tests. Rare is the lens that does not clearly produce coma on images, except at the center. None of the Takumars, for example, except possibly the macros which I haven't tried yet -- I'm hoping the "flat-field" corrections of macros will make for less coma.

beachboy2 · Posted: Wed Jun 30, 2010 12:52 pm Post subject:

JWH · Joined: 26 Aug 2009 Posts: 120 Location: Netherlands

You shouldn't use Polarization for astrography. It is a dense piece of glass and blocks alot of light. For Astrography you want to gather as much light / data as possible. Ofcourse the moon is not really cooperative but there are ways around it. The best filter to use with moon or city lights is H-Alpha. As that blocks basically all the lights coming from lights or the moon and lets alot of detail through from objects.

@Symphonic: A motorized Telescopic mount was used.
M13 is indeed a small object, but my example earlier was just to show what the least mm's you want to use is. 50mm or smaller will just give you a nice image of the Milkyway but not objects.

Also pointed out the size of M31 which is showed in the sample i've added to this post. Especially considering that luigis is using a full frame. Which means the field of view using the same setup in the sample is even larger!

luigis · Joined: 27 Aug 2009 Posts: 22

Thanks so far, I think that sharpness wide open and abscense of comma are probably the most important factors. Maybe there are some good MF lenses that I can use but I'm not sure.

Thanks for the suggestions, ideas and comments!
Luis

Attila · Expire: 2025-11-18

JohnnyC · Joined: 07 Jul 2010 Posts: 3

That shot is amazing JWH, quick question though, what does " A stack from 40x30s exposures and 20x30s darks. " mean? Does that mean you took the same shot 40 times with a 30 second exposure, then stacked them together or something in a program?

cooltouch · Joined: 15 Jan 2009 Posts: 9096 Location: Houston, Texas

I used to do some guided astrophotography many years ago -- had a 10" Meade LX3 with motorized mount, off-axis guider, and all the other necessary gear. I lived in the Los Angeles area, and it was about a 160 mile round trip for me to get to a place with truly dark skies, so I didn't make it up there as much as I liked. That was like ancient times compared to now, though. What can be done with digital outfits now is really quite remarkable compared to the way it used to be done.

I'd like to try this stacking technique one of these days. Don't have any telescopes anymore though, so I would have to make do with photographic lenses.

I've found that I can get pretty good shots of the moon with a decent 500mm lens mounted to my Canon crop body. I have to use Live View to make sure the focus is accurate. I don't use any filters, either. I think I used a teleconverter in the second shot below.

My old Meade 10" had a focal length of about 2000mm, and I found that I could adequately fill a 35mm frame with M31 at that magnification. The longest lens I own now is 650mm. But I'm thinking that, despite its considerably smaller size, resolution may hold well enough where even my 650mm f/6.8 might be adequate for some astrophotography subjects.

symphonic · Joined: 23 May 2010 Posts: 550 Location: SE Europe, Croatia

Recently I had a first try with astrophotography. Not solely my attempt though, I had two friends with me, one brought his EQ5 motorized mount and the other had a borrowed CZJ 180/2.8. And I had a 450D so we were good to go. xD

So we pointed the thing towards Saggitarius, the Lagoon nebula ( M8 ) and the Triffid ( M20 ). The result is this, not particularly handsome, but since it was a first try ever, I guess it's ok. Smile

As evidenced even in this small crop, the mount wasn't Polar aligned very good, it gave trailing stars even after 30sec...

6 frames @ISO800 and 26 sec with a 180/2.8 at 4

mo · Expire: 2016-07-30

What do you need as the most basic set up to try this?
I have the dark skies...benefit of living in the wide open country spaces in Australia or at least less than hours drive from town,I can spot the satellites,shooting stars/burning space junk or what ever they are Very Happy

Clear open skies on a good night.

symphonic · Joined: 23 May 2010 Posts: 550 Location: SE Europe, Croatia

The most basic/cheap setup to do widefield astrophotography would be a (self-made) barn-door tracker, like this with a camera and a lens of your choice (preferably a high-ISO performing one and a middle to long telephoto lens). If you're good with tools or know someone who is, a well-made barn-door tracker can be great for tracking (there's several designs, some are more advanced and allow higher exposures).
Or you can get an equatorial telescope mount with motors and a nice apochromatic scope on top of it, with a much higher budget and it's a never-ending line from then on. Very Happy

I envy you on the dark skies... and the Southern sky. Wink

mo · Expire: 2016-07-30

That "barn door" is a piece of brilliance Very Happy

I don't have the high iso the K200D is only 1600...the mid lenses I do have Very Happy

and the dark skies.At least I have some idea now...a lot more to it than just pointing a lens at the night sky.

symphonic · Joined: 23 May 2010 Posts: 550 Location: SE Europe, Croatia

mo · Expire: 2016-07-30

OM · Joined: 15 Jan 2010 Posts: 166 Location: Southern England

visualopsins · Expire: 2025-04-11

Shutter speed star trails begin to appear depends on lens angle of view. Pixel peeking reveals even with ultra wide angles.

For star charts I've used Skyglobe DOS version for years; there is a Windows version, but read the note about how to get it to work (shift-click on Start menu, shift double-click from Explorer.

There is also fantastic Celestia for virtual touring the universe, with gigabytes of additional imagery for download.

symphonic · Joined: 23 May 2010 Posts: 550 Location: SE Europe, Croatia

Stellarium - perhaps the most user-friendly app for simulating the night sky.
SkyMaps - printable monthly sky charts with a list of popular objects seen in binoculars or smaller scopes and notable events happening during the month.
Taki's star atlas - a nice detailed atlas for beginners interested in more objects.