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04-08-2015, 12:47 PM   #1
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50mm AF f1.4 for astrophotography

As a newcomer to the world of DSLR, but not photography (had a good suite of Nikon 35mm kit over 30 years ago, but family life intervened) but having borrowed my daughters K-r last year for a trip to the US I thought its time i acquired my own kit

i invested recently in a K50 with kit zooms (18-55 and 50-200) and forked out on a 55-300 for my love of snapping my local football (soccer) team games

However i really want to get some pics of the night sky and was truly disappointed with the 18-55 kit lens on the K-r when in Monument Valley last year. I guess because it has a max of f3.5

Seen a few 50mm AF f1.4 on ebay in Uk at far more reasonable price than new retail and wondered, mainly for its wide aperture if it is a reasonable buy for occasional use .. and will it work well (subject to operator error) for night sky work??

thanks

04-08-2015, 01:11 PM - 1 Like   #2
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QuoteOriginally posted by delboy65 Quote
50mm AF f1.4
That can mean quite a wide range of lenses in Pentax land. Best to be very specific on which lens unless it cannot be mistaken.

I do not do a lot of astro-photography but what little I know or read about here seems as if a much wider lens is used. 28mm or 30mm as the 50mm might be too narrow an angle of view on APS-C. Depends on what you want to shoot of course.

That said the Pentax 50mm lenses are usually quite good. I assume you are looking at the FA 50mm f/1.4? There is also a DA 50mm f/1.8 which is much less expensive and only a little slower. There are also a good number of manual focus 50mm lenses that might work well if all you are doing is astro because the auto focus is not really used.
04-08-2015, 01:20 PM - 1 Like   #3
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QuoteOriginally posted by delboy65 Quote
However i really want to get some pics of the night sky and was truly disappointed with the 18-55 kit lens on the K-r when in Monument Valley last year. I guess because it has a max of f3.5
May I suggest that you upload one of those 'disappointing pictures' together with exposure and other details (tripod? manual focus?). Chances are that your lens is better than you think, and that the issue is as much a matter of processing as a matter of lens quality. An aperture ratio of f/3.5 is not too slow to get useful results.
04-08-2015, 01:26 PM - 1 Like   #4
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Hi delboy65.
As there are so many lenses that work for different locations and times, you may want to search the threads for astro related articles and advice.
Here is a new article series:
Astrophotography Part 1 of 6: Planning the Shoot - Articles and Tips | PentaxForums.com
There is also a group here to join!
Astrophotography - PentaxForums.com

04-08-2015, 02:29 PM   #5
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During my film camera years, I dabbled in astrophotography, but haven't done much with digital. I'd suggest that a 50mm on an APS DSLR is too long for wide photos of starfields, and obviously not long enough for closer work. If you want something reasonably cheap, you might look at the "Plastic Fantastic" 35mm f2.4 AL. This is still a little long on an APS DSLR (on a full frame camera it would be very good), but not so much as the 50mm, and the aperture should be fast enough for star fields, and it is pretty sharp even wide open.
04-08-2015, 06:01 PM   #6
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There was a winning astro shot on here a month ago, shot with a kit lens i believe. I may be mistaken.
04-08-2015, 06:32 PM - 2 Likes   #7
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I would think you'd be better off looking for an O-GPS1 astrotracker rather than a fast 50. That way you could use your existing lens(es) at longer shutter speeds, as opposed to having to deal with the 50mm and its lack of extra length. You need to bear in mind, that f1.4 lens will probably still need to be stopped down to f/1.7 or f/2 to start getting usably sharp shots.

The astrotracker should be around the same price as the fast 50, maybe a hair more, but will be MUCH more useful out in the field.

Heres a shot I made with my 10-20 @ f3.5 using mine. The kit lens would probably give around the same results (only narrower, of course).

90 seconds, 10mm, propped against a rock for stability. Shot on a busted up K-30

04-08-2015, 07:25 PM   #8
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The kit lens will get you usable night shots... but I don't know about how it performs on the K-r vs. the K-50. At your widest angle of 18mm, with widest aperture of f/3.5, you would be looking at approximately 10-13 sec. for stars without any visible trailing, but the image would also be rather dark and that's at ISO 640. With the kit lens, I would suggest using ISO 800 for astro with that same 10-13 sec shutter at 18mm f/3.5.

As sagitta mentioned, the o-gps1 astrotracker would allow you to use longer shutter times, but an often times much cheaper solution is to just get a manual lens in the 20-28mm focal range (fixed prime) with an aperture of 2.8 or wider. Also, even more important is to have a way of keeping the camera pointed up and immobile.. either with a tripod or some other method, then use either a wired/wireless remote, or the self-timer to prevent camera shake.

04-08-2015, 11:29 PM   #9
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Original Poster
Thanks for the useful info everyone.

Will upload an example taken last year later when worked out how to do that (working off the tablet at moment)

The lens i was looking at is SMC FA f1.4 AF. Do see lots of old K Mount f1.7 manual lenses available. I just fancy the wider aperture.

I realise the focal length effectively gets increased due to the cropped sensor (field of view rather than actual increase), but does anyone know what the FoV ratio increase is on the K50 cropped sensor?

Have seriously considered the astrotracer, however i have read so many mixed reviews on these pages , especially about calibration issues so felt 200 ($350) a bit OTT for occasional use and potentially more grief than benefit

I also realise so much can be done in post processing these days, and that will be an important next step , but first want to get an image i can be happy with ... though finding a dark place will help that cause greatly

thanks
04-09-2015, 12:10 AM   #10
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some examples (3/4)

Pentax K-r
18mm
f5
ISO 800
84 Sec
Manfrotto Pixi mini tripod
IR Remote release
High Wycombe, UK - Dec 2014

Last edited by delboy65; 04-28-2015 at 04:35 AM.
04-09-2015, 12:11 AM   #11
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some examples (4/4)

Pentax K-r
18mm
f5
ISO 800
23 Sec
Manfrotto Pixi mini tripod
IR Remote release
High Wycombe, UK - Dec 2014

Last edited by delboy65; 04-28-2015 at 04:37 AM.
04-09-2015, 12:14 AM   #12
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Greetings from new comer

Hi everyone, I have been using pentax film and istDS cameras for casual photography for some time, and love Pentax cameras and lenses for its color and style, but have not dived deep into this, so my skills are rather mediocre. I recently found this this awesome website, hope I can improve my skills and make friends here.
04-09-2015, 12:42 AM   #13
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QuoteOriginally posted by delboy65 Quote
I realise the focal length effectively gets increased due to the cropped sensor (field of view rather than actual increase), but does anyone know what the FoV ratio increase is on the K50 cropped sensor?
The factor is 1.5 (on any current Pentax dSLR). But it's actually irrelevant; the kit-lens at 50mm and the FA50/1.4 will give the same FoV when mounted on the same body.
04-09-2015, 09:16 AM - 1 Like   #14
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QuoteOriginally posted by delboy65 Quote
The lens i was looking at is SMC FA f1.4 AF. Do see lots of old K Mount f1.7 manual lenses available. I just fancy the wider aperture.
If you want AF you should consider the DA 50mm f/1.8, the FA 50mm f/1.4 or the F 50mm f/1.4 (or f/1.7) The f/1.7s are a different design and there are arguments over which is better, but I think it is sort of like arguing over which Ferrari to buy. In any practical use you will not be able to tell the difference. I have the F 50mm f/1.4 and f/1.7 and honestly cannot tell the difference when looking at images. Pick the one that comes by in your budget. Note that one difference will be the coatings which have improves over time and theoretically the DA version should be slightly better in that regard.
QuoteOriginally posted by delboy65 Quote
I realise the focal length effectively gets increased due to the cropped sensor (field of view rather than actual increase), but does anyone know what the FoV ratio increase is on the K50 cropped sensor?
1.5x
QuoteOriginally posted by delboy65 Quote
Have seriously considered the astrotracer, however i have read so many mixed reviews on these pages , especially about calibration issues so felt 200 ($350) a bit OTT for occasional use and potentially more grief than benefit
You might want to read more on the Astro Tracer, might be what you need. Those that use it seem to really like, though I suspect there is a learning curve. I have it but have only used the GPS portion, which works perfectly.
04-09-2015, 09:23 AM - 3 Likes   #15
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FWIW, the O-GPS goes for about $200, not $350. You can find them on sale at times for even less.

o-gps1 in Camera and Photo Equipment and Accessories | eBay

The biggest two quirks (for lack of the better term) are learning where and where it won't work and how to properly calibrate it. The instructions are spotty at best in explaining both.

Since the unit uses magnetism to track, if you set up somewhere with a lot of metal in the ground (example, by the river here it used to be a mill, the ground is filled with iron slag and the tracker is almost useless there) it will not behave itself.

It will work perfectly out my apartment window, but will be thrown down on the ground level here for the reasons I mentioned above.

As for calibration, that just takes a bit of practice. You'll get to 'know' when you have and when you don't after a while. Once properly set, you can go all night without needing to retool it.

EDIT:

As another example, heres the Orion Nebula @ 300mm using a funky old 80's manual 300mm lens. This was either f/5.6 or f/8, 60 second exposure on the same borked K-30.

Last edited by Sagitta; 04-09-2015 at 09:30 AM.
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