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04-14-2015, 06:06 AM   #1
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Advice on getting KS-2 and 1-2 lens for astro

I know it is strange but I placed an order for an O-GPS1 to try astrophotography with Pentax, but not yet have any small format Pentax body yet and lens. Did have Pentax 67 and 55/90/135/200/75-shift/300old for 67, And some Hasselblad old C lens. As my Nikon lens cannot be used, need to fine a body and 1-2 lens.

I targeted KS-2 as it got the flip out screen. I knew quite a lot used the K5 but I need to point to 60 degree + to the sky. hard for the neck.

I read a bit and totally confused by this DA, Limit, ... CanI ask for advice on which 1-2 lens to start with. Do not mind manual or heavy (Still use Pentax 67). Did like one for wild field and one for closer a bit (but <=200mm). Old lens is fine. manual focus is fine. Pure for astro experiment. (I have others like iOptron tracer and the astrotrac but both need sort of north star which I cannot easily see in my place).

Many thanks in advance.

04-14-2015, 06:33 AM - 1 Like   #2
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Maybe Samyang 14mm F2.8 ? or the 16mm F2 at 2.8 ?
04-14-2015, 07:43 AM   #3
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No experience with it, but you can consider Pentax 67 Lens to Pentax 35mm K-Mount Body Adapter 37954 B&H for the longer end
04-14-2015, 02:50 PM   #4

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67 lenses on the k-s2 is pushing it a bit (tried some out on a k-3). To be honest, it makes sense to mount 67 on 645, but hardly any sense on aps-c. Aside from being insanely large, the IQ doesnt stand up to 24mp in a sensor area approximately 10x smaller than 67 negs. When decent k/m/a primes can be had for less (faster, lighter, cheaper), it makes 67 glass seem extravagent (the bokeh on the 105 f2.4 is quite nice, although it's a touch soft with odd colours on aps-c)

If you already have the lenses, then you might as well buy an adapter. Otherwise, it's pretty pointless.

Fa31, fa43, da*55, fa77,da*200, da*300. Those are the premium level primes (expensive, but fantastic performers). If you can afford only one lens from that list (second hand probably!), it'll be worth it. Da*'s are weather sealed, the fa limiteds are not (but most people *love* them)

The da limiteds are fine lenses (small, with fantastic image quality, although with smaller apertures than the others). If you want an all rounder lens (with auto focus), then the da21, da35 macro, or da40.

The samyangs look pretty good (not used one myself though, and they're manual focus, but do have the 'a' setting for auto exposure). They're quite big though!

The two cheap da primes (da35 f2.4, and da50 f1.8). Cheap, cheerful, and pretty decent.

If you want super cheap, then look towards the 'm' series. The m50 f1.4 can be had for a bargain price, and 200mm primes are super cheap. You'll be limited to fully open all the time (in most modes), but you can do stop down metering if you use 'm' (manual) on the camera + the green button (beware of lenses that have been butchered by canon users though!).

The 'a' series are basically the same as the 'm', except they can auto meter the light. The prices tend to be a bit higher (because they are more useful).

I'd recommend something like the fa43, da21, or da35 macro - just to have something superb in your bag (or if your budget allows, the da21 and the fa43!). Then maybe an m50 f1.4, and either an m135 or m200.

04-14-2015, 03:06 PM   #5
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When using the o-gps1, the tracking/exposure time available to you decreases with increased focal length. Longer focal length will also magnify any tracking errors. Conversely, if you use extreme wide angle lenses, the problem starts to creep in on longer exposures where axial vs planar tracking error causes some stars to trail when others do not. The Samyangs mentioned by ChristiC are very good, especially with axial instead of planar tracking. if you're just starting with it you may want to stay between 28-200mm I have used the 6x7 200mm (old style) on a K50 with the adapter sterretje mentions above, and it actually performs pretty well at f5.6. see second review: SMC Takumar 6x7 200mm F4 Reviews - 67 Telephoto Primes - Pentax Lens Reviews & Lens Database i also have a 6x7 105 2.4, but found it unsuitable for astro work.
The old manual M50 and A50 1.7s are inexpensive enough, and perform well for astro as they have far less coma than the 1.4's do, especially good staring about f2.8 or so.

Note: Since critical focus is essential for astro work, I find it easier to focus at the aperture I will be using. (also makes it much easier to judge acceptable levels of abberation) Because of this, I actually prefer 'leverectomied' lenses for astro work. Not that I would want to go cutting off any levers, mind you...
04-14-2015, 03:19 PM   #6
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with the o-gps1 I use a sears 135/2.8 (caught comet lovejoy with it) and a sears 70-200/4 with varying results and exposure times but I need more experience with the mysterious device and as the weather is now getting warmer clear skies on the weekends I look forward to......I will use my sears 28/2.8 with the o-gps to shoot the galactic plane until I get some dollars for a 14/ is really a matter of what you like and works for you as there are too many options to say 'hey man this is best bar none'
good luck and happy shooting! I look forward to the adventure as well
04-15-2015, 04:38 PM   #7
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Many thanks for all the good advice.

For pentax lens, I probably tried a bit M lens first if it can deal with 20M APS-C resolution. Would have the new collapsable kit lens as well. Wait for 1 month for the o-gps1 arrived fist then go to get it. The price seems falling already and hence wait a bit might be good.

6x7 mm is not that sharp but it is light relative to its size. The best two I have is the 55 and 200, with the 90. Never got the 105 2.4. I would try the adapter for this and Hassey as well as I already have these lens in any case. (The Hessey even though it is 1960 C lens seems resolve well with my OMD and Nikon etc. Hence I suspect it is of higher resolution. For film, 67 lens is good enough and got its only different transparent look. The Hessey lens seems to add a lot of colours. Like them both and take them out from time to time.)

04-15-2015, 07:59 PM   #8
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Whatever else you get, I think you should definitely get one of the M or A 50mm lenses, since they're fast, they're excellent optically, and they're and really cheap-- you can find them for $100 or less on KEH. You'll have to work with manual focus and possibly manual aperture, but you can't beat the ratio of price to usefulness.

04-16-2015, 01:01 PM   #9
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QuoteOriginally posted by dng88 Quote
I read a bit and totally confused by this DA, Limit

you've been given some pretty specific advice, so I'll start with the basics...

Every Pentax lens ever made can be used, though everything named "Takumar" or "m42" will require an adapter, maybe not very simple for a beginner.

DA, DFA, DAL, HD lenses are the most recent. They are "made for digital". They are auto everything (AF, exposure, etc). Limiteds and STAR (marked *) are specific lenses in these categories that are higher-quality. Limiteds are small primes, STAR are larger aperture lenses, weather sealed and often zooms. Any lens marked STAR or WR will be weatherproof.

F and FA lenses are the first two "auto everything" lenses, made for film but fully usable still. The primes are excellent, the zooms... it depends. There are STAR and limiteds in those lines too.

A lenses are auto exposure, manual focus. A nice compromise.

M and K lenses are fully manual. Manual exposure and AF. You can set the aperture on the lens and ask the camera to meter the shutter speed. They are generally extremely well made, durable.

so there you are.

Now, you want to do astrophotography. Do you want to couple the camera to a telescope, or shoot wide views of the sky?

For the former I can't help you. For the latter, there are many choices, but I'd suggest a wide lens, 21mm or wider if possible. There are many options to choose from. Pentax has a few nice primes (DA21, DA15, DA14) and there are many, many zooms covering these ranges. Some third-parties also make good lenses.

It might be advisable to decide what ELSE you want to do with your lens or lenses. That might guide the suggestions a bit more precisely.
04-16-2015, 03:05 PM   #10
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These are good and clear advices. Many thanks again.

I want the Pentax to avoid the issue in urban sky where you can see only some stars in some part of the sky and not others. One 2x, 5x, 1xx and 2xx would be my target lens. Based on the advice, the 2xx could be covered by the 200mm of Pentax 67 with adapter. In fact as the maximum that O-GPS1 probably is the last to try.

5x I looked at KEH and found three 1.4 old lens, all sounds similar and around $100. May try one of those.

2x I saw a 28 F3.5 ... not sure.

Would try to look at those newer DA 2x lens as well.

Thanks all!
04-17-2015, 10:08 PM   #11
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Arrived too soon:

Need a body and lens!

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