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09-05-2016, 06:53 AM   #1
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Pentax 300mm lenses for Astrophotography

I'm struggling to find much info on how well the Pentax 300mm primes work with Astrophotography, I'm sure some of you must have used them (and have probably posted your comments & results) but today google has not been my friend

I no longer have a DA*300/4, but do have an F* (and FA*) 300/4.5 - and as I'm happy shooting at maximum aperture for daytime subjects I was wondering whether there is a need to stop down (to reduce any potential abberations) for astro shots?

I did try an A* 300/4 a couple of years ago without much success, but I'm hoping the F* will be a better performer

Any tips, links to posts, etc. very much appreciated

09-05-2016, 09:03 AM   #2
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I have shot the moon and a few other things in the sky but I don't really know much about Astro photography to respond to this fully. I paid mine with Teleconverters as well so that complicates my experience.
09-05-2016, 11:04 AM - 3 Likes   #3
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With the DA*300 I made this. In my experience, the DA*300 is a fantastic performer, even wide open, as the F* should be.


The galaxy of Andromeda by Michele Remonti, su Flickr

Last edited by aiki76; 09-05-2016 at 11:14 AM.
09-05-2016, 11:52 AM   #4
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Yes, the DA*300 is my main astro lens, used mainly for comet hunting. It is sharp throughout its field with no appreciable aberrations, even wide open. I stop down one notch just to get rid of any residual aberrations. The F and FA versions are likely just as good. Here is an example:



09-05-2016, 06:37 PM   #5
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Depends what you are wanting to capture. As with basically any telephoto lens you can expect some chromatic aberrations (purple fringing) wide open though not as bad as from before the development of ED glass. The extra glass elements that a telephoto lens has over a refractor telescope makes it harder to keep all wavelengths in focus, hence the fringing, but how much a problem this is will depend a lot on what you are shooting and how much colour you want to retain.

Personally, though, I find 300mm to be a bit of an awkward focal length - too long to capture constellations and star fields, too short for all but the largest deep space objects (eg. Andromeda and the Magellenic Clouds). You'll get nice shots of the larger nebulae, but you'll miss detail compared to a 400mm, which I view as the minimum for this stuff, though 500mm and up is where you really want to be (cropping is an essential part of DSO photography with a DSLR, the more you can get before cropping the better, though really long focal lengths bring new problems). By then, however, you are looking at a very different class of gear. That said, the best gear is the gear you have, and you may find it really works for you.

Another consideration is tracking. At 300mm you would be pushing astrotracer to (if not a little beyond) its limits, so beware of that is this was you plan. You will be wanting to move to a equatorial mount of some sort. Good news is that at 300mm tracking will be pretty forgiving on a proper mount.
09-08-2016, 01:31 AM   #6
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Thanks for the responses - I do want to experiment with Andromeda and the like, hence the choice of focal length - my main concern is over whether I need to stop down at all (I know I have to with some "wide field" lenses to reduce Coma), as f4.5 is already 1/3rd stop slower than the A* and DA* and I know a lot of this is about light gathering.

Some nice examples posted in the thread too - very encouraging
09-08-2016, 10:27 AM   #7
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QuoteOriginally posted by LennyBloke Quote
Thanks for the responses - I do want to experiment with Andromeda and the like, hence the choice of focal length - my main concern is over whether I need to stop down at all (I know I have to with some "wide field" lenses to reduce Coma), as f4.5 is already 1/3rd stop slower than the A* and DA* and I know a lot of this is about light gathering.

Some nice examples posted in the thread too - very encouraging
Sure, catching sufficient light is essential. But with long focal lengths and thus, limited exposure times with the Astrotracer, you will also in most cases need stacking and post processing for satisfactory results. You may find this guide useful: Accueil / Albums | PhotosSteph

Also take a look at this guy's album with 200 and 300mm deep-sky photos.
09-09-2016, 09:23 AM   #8
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QuoteOriginally posted by Stone G. Quote
Sure, catching sufficient light is essential. But with long focal lengths and thus, limited exposure times with the Astrotracer, you will also in most cases need stacking and post processing for satisfactory results. You may find this guide useful: Accueil / Albums | PhotosSteph

Also take a look at this guy's album with 200 and 300mm deep-sky photos.
That's a nicely concise site for advice - some can be so complex that they lose me very early on - his gallery is pretty impressive!

I had a quick bash with the FA*300 last night, didn't get long before the clouds started to cover but once I got the focus about right and worked out the maximum exposure (rarely do I get anything close to the maximum time the AstroTracer suggests) I did manage to get this one. No idea where it is, but maybe the "Beehive Cluster"?



Again, thanks for the tips

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