Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-30-2021, 02:51 AM   #1
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2014
Photos: Gallery
Posts: 141
Wide Angle lens suggestion / Space inside the mirror box

Hello all, I just thought I'd make a suggestion with regard to a potential wide angle lens for the 645Z and 645D, as well as perhaps for the film bodies.

Special emphasis on potential. I have no idea whether it might work and it may be a dead end, but it's just an idea to toss out there; I haven't seen mention of it anywhere else or another person trying it, and with the rarity of the 25mm f4 and the fairly regular posts of people requesting wider lenses, I thought it would be worth suggesting.

The Samyang 24mm f3.5 tilt/shift lens has a fairly generous mount distance once its tilt/shift mechanism has been removed. I own one, and have adapted it to a Mamiya 645 mount to use with a digital back ( sorry if that makes me a traitor of sorts! I still shoot with my K-1! ). The conversion itself is fairly straight-forward, and it took me an afternoon on a lathe and a milling machine to machine up the adapter tube.

The problem is the rear lens element. With the Mamiya 645 flange distance, the rear element protrudes slightly beyond the bayonet mount when focused to infinity. The Mamiya 645 body has probably about 10mm of clearance at the front of the mirror box, so the rear lens element easily clears the arc of the mirror and isn't a problem.

I have no idea what kind of clearance the 645Z and D might have at the front of their mirror box, and it would need to be as generous as the Mamiya; if not a little more due to the extra 8mm or so flange distance of the Pentax 645 mount. Maybe someone with a camera body could take some measurements, and we might be able to determine if it could work?

The lens itself is okay. Not great, not bad, but okay. It's never bitingly sharp, but good for its price! I can only judge from the copy that I have, but anything below f11 seems to be a mostly a waste of time ( at least adapted to the Mamiya ). I usually use it at f16 or f22 ( or somewhere inbetween - my lens lost the detent in the aperture ring during the adapting process ), where it becomes surprisingly competent - sharp enough nearly right across the frame on a full digital 645 sensor, and it holds up pretty well at 80 megapixels. I have discussed this lens with people who have used it on the Fujifilm GFX 50mpx bodies who have echoed the same thing - competent, but not stellar. It takes 82mm filters, but vignettes heavily when I use them. I devised a mount that slides over the rear lens element that holds a 37mm ND filter, but this degrades the image quality markedly ( probably due to the fact I used a cheap ND filter as I couldn't find a good brand that made them that small and didn't even know if it would actually work ). On the 44 x 33 sensor I wouldn't expect the use of 82mm filters to vignette.

For the money and a little bit of time, it could be a worthwhile consideration if someone was looking for something wider than what the 28-45 offers, or if you can't afford the 25mm or the 28-45 and only have the 35mm as your widest option ( and have the ability to machine an adapter to suit ).

Just a thought. Open to ideas!

Attached Images
     
11-30-2021, 06:48 AM   #2
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 22,754
Have you considered the FA 33-55 as a not quite as wide alternative?

SMC Pentax-FA 645 33-55mm F4.5 AL Reviews - 645 Zoom Lenses - Pentax Lens Reviews & Lens Database

Cheap. Good image quality at the same f stops you mentioned.

Yes itís not as wide, but itís much wider than the alternatives.

Alternately Iíd look for a different lens to adapt with a longer flange focal distance natively to make clearance less difficult.

---------- Post added 11-30-21 at 09:03 AM ----------

The Kiev 88 or Pentacon Six Arsat 30mm fisheye would likely work well. These arenít expensive and could be defished still yielding very wide results. The flange focal distance is larger than the Pentax 645 and should be Possible to adapt without mirror clearance concerns.
11-30-2021, 07:03 AM   #3
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2014
Photos: Gallery
Posts: 141
Original Poster
QuoteOriginally posted by UncleVanya Quote
Have you considered the FA 33-55 as a not quite as wide alternative?
Yes, I have considered this lens, but not for the purpose that you may be thinking!

I probably didn't make it very clear in my original post, but I don't actually own a 645Z or D. It was a suggestion for those who do and who are pondering whether or not something wider is available or viable.

I am considering picking up a copy of the 33-55mm and adapting it to Mamiya mount, as it is a useful range for a zoom. The medium format camera I shoot with has a sensor that is a bit bigger, so my Samyang 24mm is somewhere around the equivalent field of view of a 16mm lens in 135 equivalence, which is pretty useful to have in my kit.

If it was able to be adapted to the Z it would probably be around the 18/19mm equivalence, which would definitely be a great focal length to have available.
11-30-2021, 07:10 AM   #4
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 22,754
QuoteOriginally posted by Focusrite Quote
If it was able to be adapted to the Z it would probably be around the 18/19mm equivalence, which would definitely be a great focal length to have available.
Gotcha. The depth of the rear element in the body seems likely to foul the mirror but Iím not sure. The Arsat 30mm with the fisheye perspective may give even wider results and is well respected and has a more easily adapted mount. Iíd be curious to know if youíve tried it.

11-30-2021, 07:26 AM - 1 Like   #5
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2014
Photos: Gallery
Posts: 141
Original Poster
QuoteOriginally posted by UncleVanya Quote
The Arsat 30mm with the fisheye perspective may give even wider results and is well respected and has a more easily adapted mount. I’d be curious to know if you’ve tried it.
At the moment, unfortunately not. I think I've heard it mentioned on the forum before, but have never seen or handled one. Fisheye lenses aren't really my cup of tea and I'm not sure how much detail might be lost with the de-fishing process in post. I've seen similar posts about a 24mm fish-eye lens that people were using for Mamiya 645 cameras as a way of having an ultra-wide and getting around purchasing the 28mm Mamiya wide-angle, which is one of the more expensive legacy lenses. However, once the de-fishing in post was complete I think it ended up being not quite as wide anyway with worse IQ, so I'm not entirely sold on the idea unless that particular perspective / artistic look is what you are going for. With my own efforts at adapting lenses to Mamiya mount I'm sticking with what I know for know, which are Pentax 645 lenses; however I am certainly curious if there are other options out there!

QuoteOriginally posted by UncleVanya Quote
The depth of the rear element in the body seems likely to foul the mirror but I’m not sure.
If anyone is actually interested in finding out, they will need to take some measurements from the mount on the camera body to the lip of the mirror, nearing the top of its arc. I can try and get some measurements off my Sammy 24mm and then we could do some simple math and see if it might work. Could be useful to someone!
11-30-2021, 08:22 AM   #6
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 22,754
The distance seems tight:

https://commons.wikimedia.org/wiki/File:Pentax_645Z_cutaway_2015_CP%2B.jpg
11-30-2021, 11:17 AM   #7
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,052
QuoteOriginally posted by Focusrite Quote
... I devised a mount that slides over the rear lens element that holds a 37mm ND filter, but this degrades the image quality markedly ( probably due to the fact I used a cheap ND filter as I couldn't find a good brand that made them that small and didn't even know if it would actually work ) ... .
Probably due to the fact that the lens system has finished making all the rays to each point on the focal plane get there at the same point in time/phase, and an unplanned added filter of finite thickness makes the more angled rays take longer. In certain Pentax (and the Arsat fisheye) the optical system is designed for an internal or rear filter and a clear "filter" is provided when an actual filter is not being used. A Wratten filter might work better, but will still cause aberrations.

12-01-2021, 12:30 AM   #8
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2014
Photos: Gallery
Posts: 141
Original Poster
QuoteOriginally posted by UncleVanya Quote
The distance seems tight:
Agreed, it would be close. That's a nice cutaway, plenty of space for an IBIS unit?!

QuoteOriginally posted by kaseki Quote
Probably due to the fact that the lens system has finished making all the rays to each point on the focal plane get there at the same point in time/phase, and an unplanned added filter of finite thickness makes the more angled rays take longer. In certain Pentax (and the Arsat fisheye) the optical system is designed for an internal or rear filter and a clear "filter" is provided when an actual filter is not being used. A Wratten filter might work better, but will still cause aberrations.
Makes sense to me!
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
645d, 645z, camera, clearance, distance, element, flange, idea, lens, machine, mamiya, medium format, mirror, mount, pentax, reviews, sensor
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Space X Puts The US back In Space Racer X 69 General Talk 13 05-31-2020 04:12 PM
Suggestion for wide angle lens and travel lens VCtwo Pentax SLR Lens Discussion 11 03-23-2019 12:03 PM
Suggestion for a wide angle prime (FA or M) yusuf Pentax SLR Lens Discussion 3 08-18-2013 09:45 PM
Wide Angle Lens suggestion bdparker Pentax SLR Lens Discussion 15 11-13-2012 02:39 PM
What equipment do I take? Wide angle suggestion? mgvh Troubleshooting and Beginner Help 23 12-19-2010 07:28 PM



All times are GMT -7. The time now is 04:41 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top