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06-26-2020, 11:20 AM   #1
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Pentax K-1 Which lens to zoom up the night sky?

Hello guys,

I was looking for something that could do better job than a 200 mm lens - actually my best tele lens. I heard about mirror lenses which can reach 500-1000 mm and they should be cheap but I don't know them much. I´d need a suggestion for a converter too. Pentax does not offer much, over 300 mm and I don´t know other brands. May someone what could look for?


Thanks!

06-26-2020, 01:48 PM   #2
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The Pentax-DA* 300mm F4 ED [IF] SDM covers a full frame image circle, no? Even though it's designated as a DA, it's compatible with the full-frame K-1 (I think).
06-26-2020, 01:55 PM   #3
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My 200 mm is an old FA 4,7-5,6 and gives me purple fringing with Jupiter and Venus but not bad for Moon. I´d like to go closer to planets and stars. Actually FHD videos looks much better than shots. What about extensors on my 200 mm for example?
06-26-2020, 02:01 PM   #4
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Putting a teleconverter on a slow lens will only make it slower and have harder time to capture enough light to exposure a decent looking image.
Getting a fast lens above 300mm is very expensive...

06-26-2020, 02:50 PM   #5
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Check out some of the astronomy sites (equipment sellers) who offer long focal length lenses as telescopes which can be used with camera. These usually come at a cost but offer faster lenses designed for astro work. There are some reflecting scopes which perform very well but these can be quite high priced, though they are a solution for the person who wants to specialize in astro-photography. In comparison, few camera lenses are available in long, fast versions, and if they can be found, their price would compare to specialized astro-lenses, the latter which may have more to offer in the final comparison.

https://www.telescope.com/catalog/product.jsp?productId=113910

https://www.celestron.com/pages/celestron-dealers

https://www.astronomics.com/
06-26-2020, 02:57 PM   #6
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Lots of astro work is done with mirror lenses. Just get a good one (such as the Rubinar 500/5.6). Remember that the donuts are in the out-of-focus areas. There is no bokeh in astrophotography. One issue, though, is that the overhang of the flash unit on many DSLRs will prevent the lens being mounted unless a short extension tube is used. This will affect infinity focus, so you then have to adjust that. No big deal, but easier with a body that is flat at the front.
06-27-2020, 02:22 AM - 7 Likes   #7
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The DA* 300 is a good choice for a try on deep space objects.
Extreme sharp and good contrast, f4 is rather fast and the lens is small and lightweight - so very handy in the field!

Here is a first try from December 2019 - the Andromeda galaxy with the K1 and DA* 300 at f4 and ISO3200
For there is a bad light situation in my home town, this is a stack of about 100 shots, each at 20s (I think longer exposure is possible ...depends on the quality of the calibration of the astrotracer)
The spikes at some stars is a result of post processing.
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Last edited by bratzmahn; 06-27-2020 at 02:46 AM.
06-27-2020, 04:03 AM   #8
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QuoteOriginally posted by FozzFoster Quote
Putting a teleconverter on a slow lens will only make it slower and have harder time to capture enough light to exposure a decent looking image.
Getting a fast lens above 300mm is very expensive...
I have a Pentax FA 100 mm Macro WR, how would it work with a teleconverter?

06-27-2020, 04:18 AM   #9
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QuoteOriginally posted by corvaz Quote
I have a Pentax FA 100 mm Macro WR, how would it work with a teleconverter?
I think that will not be a big step forward...aperture shrinks to f4 and focal lenght "only" expands to 140mm. (with the Pentax 1.4x converter)
But: just try it! Due to the stacking (aligning the pictures) the result will be slightly cropped.
I wonder how the new 70-210mm f4 will do this job
06-27-2020, 09:03 AM   #10
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QuoteOriginally posted by bratzmahn Quote
I think that will not be a big step forward...aperture shrinks to f4 and focal lenght "only" expands to 140mm. (with the Pentax 1.4x converter)
But: just try it! Due to the stacking (aligning the pictures) the result will be slightly cropped.
I wonder how the new 70-210mm f4 will do this job
Sorry didn't say that my 100 mm is F2.8, if it can become 200 mm with teleconverter I might use it instead of my FA F4,7-5,6 80-200mm in any situation. I can't carry big stuff such as huge telescope so I was looking for a compromise little light cheap.
06-27-2020, 01:13 PM   #11
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QuoteOriginally posted by corvaz Quote
Sorry didn't say that my 100 mm is F2.8, if it can become 200 mm with teleconverter I might use it instead of my FA F4,7-5,6 80-200mm in any situation. I can't carry big stuff such as huge telescope so I was looking for a compromise little light cheap.
I know this lens...but I thought you will use the 1.4x converter. Then the aperture changes the same as the focal lenght! So from f2.8 you'll come to f4! If you use a 2x converter it will be f5.6! That's not a great deal...my opinion.
But what is wrong with your 80-200mm lens? Have you tried it for astrophotography?
06-28-2020, 09:10 AM   #12
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QuoteOriginally posted by bratzmahn Quote
I know this lens...but I thought you will use the 1.4x converter. Then the aperture changes the same as the focal lenght! So from f2.8 you'll come to f4! If you use a 2x converter it will be f5.6! That's not a great deal...my opinion.
But what is wrong with your 80-200mm lens? Have you tried it for astrophotography?
Here I´ve found a good guide for teleconverter Pentax K-Mount Teleconverter Guide - Articles and Tips | PentaxForums.com
My 80-200 mm is fine when I use for video usually at 80 mm but when I take bright planet as Jupiter or Venus I got purple fringing and wierd distorsion of light. Then 200 mm is not enough to focus on a single object than moon.
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