[soycory]

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Would an old manual macro lens be better for astrophotography due to the longer focus throw allowing for more precise focusing? Sorry... wasn't sure if this is a beginner, macro, lens, or astrophotography question...

[Obin Robinson]

Regardless of the focus the best thing to have is a flat field all the way across. I experimented with many different DSLR lenses and found them all to be inadequate. 35mm SLR lenses are a little better. The best bet though are adapting older medium format lenses. You can use Pentax 67, or Mamiya 645 lenses. Just to show you how good that medium format lenses can get:


http://www.skyandtelescope.com/astronomy-news/little-scope-makes-big-finds/


... you can find extrasolar planets with them.


obin

[digital029art]

Would an old manual macro lens be better for astrophotography due to the longer focus throw allowing for more precise focusing? Sorry... wasn't sure if this is a beginner, macro, lens, or astrophotography question...

Longer focus throw is really nice for close up work, but what you want is a properly calibrated infinity focus and preferably a dead stop at infinity. This way it's easy to work in the dark and most lenses will be sharp across the frame at infinity. Other things to look for is a bright max aperture and near absence of coma and low spherical aberration so that stars look like points instead of weirdly shaped lights. A tracking mount and or the O-GPS1 module (Pentax) would be good to have too!

[Obin Robinson]

Other things to look for is a bright max aperture and near absence of coma and low spherical aberration so that stars look like points instead of weirdly shaped lights. A tracking mount and or the O-GPS1 module (Pentax) would be good to have too!

That's why medium format lenses work so well. These were taken with Pentax 67 lenses:
Wide-field CCD Images


Take a look at these too:
Pentax Takumar 67 200mm f/4 | AstroBin


Here's some Mamiya 645 photos:
Mamiya 80mm 1.9 | AstroBin


Mamiya Mamija 300mm | AstroBin


You get razor sharp pinpoint stars all the way across the field.
obin

[TomTom]

Would an old manual macro lens be better for astrophotography due to the longer focus throw allowing for more precise focusing? Sorry... wasn't sure if this is a beginner, macro, lens, or astrophotography question...

Some of the other posters on astrophotography questions have pointed to this site for info on astrophotography. Here's a link to the same guy's spreadsheet on lenses.

[Obin Robinson]

That guy who did the spreadsheet (and the link) put a bit too much thought into how to avoid star trails while ignoring some really excellent lenses. If you want to avoid star trails then get an EQ mount or make a barn door tracker. Here's options:


Vixen Polarie:
Vixen Optics- Polarie Star Tracker for Astrophotography


Kenko Skymemo:
Hutech Astronomical Products - Kenko Sky Memo Tracker


Astrotrac TT320X:
Shop at OPT - AstroTrac TT320X AG AutoGuiding Tracking Mount - OPT Telescopes


iOptron Skytracker:
iOptron


Barn Door ("Scotch") tracker:
Make a Scotch Mount: From Star Ware 1st edition


Of course you can stick with the short exposures but the results will be a million times better with a simple EQ. I've also seen older Celestron fork mounts adapted for DSLR usage when put on a simple wedge. These can actually achieve incredible results for a very low cost:
Celestron Fork Mount with Quartz Drive Control System and Hand Controller | eBay




obin

[dms]

Macro lenses are typically highly corrected (for m=0.1 and larger) and often are a good general use lens--but they tend to be slower and not as good as a non-macro prime at/near to infinity. Also the longer throw on macro is at the macro end--the near to infinity throw is likely less.

[splash_fr]

Does anybody know hoe good the Pentax GPS-thing is compared to real trackers? 2min schould be doable with 200mm, shouldn't it? would be a bit lighter...

[Gimbal]

2min @ 200mm, maybe, but probably not. It is often better to settle for a shorter time (with a higher success rate) and then stack the result. It is very frustrating to wait for several minutes and then find out that the time was wasted.

[Obin Robinson]

Does anybody know hoe good the Pentax GPS-thing is compared to real trackers? 2min schould be doable with 200mm, shouldn't it? would be a bit lighter...

The Pentax GPS is designed for simple wide-field astrophotography using nothing more than a basic tripod. It is not a viable replacement for an equatorial tracking mount. It beats having nothing though.


obin

[splash_fr]

Hmmm...

OK, thanks :-)

[cstoner69]

I had the gps attachment and sold the gps attachment. It is ok for what it is but fiddly to use and also 2 mins for 200mm will be at its limits if even possible from your location and where you are pointing at the sky. However taking 10 x 20 seconds then stacking in dss is easily possible and will probably get you better results

[splash_fr]

I use the gps thing anyway for the coordinates in the EXIF. I might as well try it out with my P67 lenses (55, 75, 200). I only used it once with its astrotracer. I tried the 35ltd and the 15ltd. I liked the 35 macro but not the 15. I think I#ll try to find myself a P67->K adapter an give it a shot, not too much investment involved...

rgds,
Gerd.

[fwcetus]

Some macro lenses might be useful, more for their flat fields than for any long focus throw. However, most macro lenses are fairly slow, requiring longer exposures (requiring more precise tracking).

[Actually, I also just have to mention that, when I first read the thread's title, I chuckled a bit -- it seemed that macro astrophotography would require some significant space travel, right? - LOL.]