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04-06-2017, 12:51 PM   #1
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Pentax lenses on a Sony A7

Hi Guys,

Looking for some advice...

Im a sony user, all my kit but one lens are primes. Nothing wrong with my one zoom i have (70-200 f4) but compared to my (mostly) zeiss primes it constantly feels like a compromise - and its a lot of lens to carry round when I also carry a 100mm prime too.

So, my current setup is... 18mm 25mm 35mm 55mm 100mm and now Im looking for a 200mm (and ill probably be happy).

As many of you may know 200mm primes are pretty light on the ground, but I have read some good things about the Pentax SMC FA 645 200mm f/4 - its light enough for my needs and the handful of reviews Ive red say its a great lens.

So anyway, can anyone help me out with a few questions?!

1 - will a 200mm medium format lens result in (more or less) the same field of view as a 200mm full frame lens when mounted to the A7?

2 - Is f4 on a medium format lens (more or less) similar to F4 on a ff lens when mounted to a A7?

3 - I dont care about autofocus at all, this lens will be used for landscape and ill manual focus everything. With that in mind does anyone know what the focus throw is like on this lens, and how responsive it is when manually focusing?

I have a couple of adapted canon lenses, and I use them fine, i have no experience with adapting anything like a Pentax lens so any thoughts or comments would be greatly appreciated!

04-06-2017, 01:07 PM   #2
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1. focal length is just a number. You can use any type of lens, field of view will be the same on same focal length. What will you see depends on camera, not on lens. It is crop factor.
But you will have some vignetting if you use apsc lens on ff or ff on medium format.
2. the same here, it does not affect by matrix type.
3. Sometimes you may need some adapter to be able focus it. I am not sure here. I have never ever had medium format lens. But some (many) time ago I had pentax *ist DL, my friend had manual film nikon. He was focusing faster. He was even able to turn frame faster or silimar to my ist DL burst speed

Last edited by flaotte; 04-06-2017 at 01:40 PM.
04-06-2017, 01:19 PM   #3
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As long as you can find an adapter you will be fine. Find the adapter first though. Your success depends entirely on that.

ƒ4 is the same on all systems.... the equivalence folks are a little crazy and confusing on this point
200mm is 200mm. All you have to know is what field of view it gives you on the system you are using. If you are buying to because you have a 100mm lens and a 200mm lens is your next logical choice, everything is good to go.
04-06-2017, 01:20 PM   #4
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Essentially, field of view arises from the lens focal length and the size of the image sensor or film frame. The only other limitation is any masking that may occur within the lens if it is designed for a particular size of sensor. Your proposal to use a lens designed for a larger sensor avoids the latter issue.

You'll need a Pentax 645 to Sony adapter, or, if one of those isn't made, a 645 to K-mount adapter, together with a K-mount to Sony adapter.

04-06-2017, 01:44 PM   #5
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645 is not K-mount, but medium format. Answers 1 and 2 are Yes. Only problem is the lens renders a bigger image circle than the sensor of that camera, so there will be extra light bouncing inside the mirror box. This can cause lower overall contrast. I suggest you use a really tight lens hood
I don't know who makes 645 to Sony adapters, but hope it works out for you
04-06-2017, 01:46 PM   #6
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I shoot both with an A7 and a K-1, Mushymatt.

The DA 200mm f2.8 is another you could use - Normhead owns one.

It has no aperture ring so your adapter would need to have one - something like the Novoflex.
04-06-2017, 02:32 PM - 1 Like   #7
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I wouldn't buy a meduim format lens they are very heavy just get a SMC Pentax 200mm F4

04-06-2017, 02:53 PM   #8
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A number of good 200mm options around: pentacon/meyer 200mm f4; tamron adaptall 200mm f3.5 ( 3 varieties); takumar 200mm f3.5 and 4; jupiter 21...check the reviews.
I have some comparison pics on my test page:

Image comparison classic 70-210mm vintage lenses: vivitar series 1, tamron SP

and actually one of the best performers at 200mm (210mm), even compared to the primes, is the tamron adaptall SP 70-210mm 52A.
04-06-2017, 03:03 PM   #9
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QuoteOriginally posted by mushymatt Quote
As many of you may know 200mm primes are pretty light on the ground
Welcome to the Pentax Forums!

I have a couple 200mm manual focus primes (f/3.5 and f/4) on my shelf that will adapt to your A7 and which were designed to cover the 24x36mm frame. I paid $35 for one and $45 for the other. The focal length is not particularly scarce and good deals are available if you are willing consider legacy glass. For example, there is what appears to be a very nice OM Zuiko 200/4 with matched TC on eBay BIN for $75 USD.

Olympus OM Zuiko 200mm F4 with matched OM Zuiko 2X teleconverter | eBay

There are also two Pentax-M 200/4 being offered at less than $50 USD.


Steve
04-06-2017, 03:16 PM   #10
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There are also two Pentax-M 200/4 being offered at less than $50 USD.


Cheeep but good, also a Ricoh branded 200mm F4 is the same and they are Cheeeeeeper!
04-06-2017, 03:35 PM   #11
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QuoteOriginally posted by marcusBMG Quote
I have some comparison pics on my test page:
I just looked at your comparisons and must say that the Meyer 200/4 is pretty impressive at f/8 even when put up against the Tamron SP 70-210/3.5 (19AH).
04-06-2017, 03:47 PM   #12
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Yes Steve I agree the Meyer is a sharp lens. So is the takumar (I only have the f3.5) - not much to choose between them resolution wise but rendering is different.
Actually I didn't think the 19AH was the best at 210mm, it's good but for me it really shone at the other end of its zoom range (click on the title to go to the overall review page).
04-07-2017, 12:14 PM   #13
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Hi guys cheers for your fantastic advice!

Ill admit Ive used a few old cheap lenses and they have never come close to touching a modern prime (center fine, corners lacking) which Is why Im considering the MF lens.
04-07-2017, 05:27 PM   #14
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QuoteOriginally posted by mushymatt Quote
Hi guys cheers for your fantastic advice!

Ill admit Ive used a few old cheap lenses and they have never come close to touching a modern prime (center fine, corners lacking) which Is why Im considering the MF lens.
Ummmmm...you would have a sweet spot advantage, but the dirty secret is that many medium format and large format lenses don't perform that well on a severe crop. Servicing a large image circle comes at a cost.


Steve
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