Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-12-2020, 02:27 AM   #1
Site Supporter
Site Supporter




Join Date: Sep 2006
Location: midwest, United States
Photos: Gallery | Albums
Posts: 5,712
Arsat 30 field of view on Pentax 645 digital?

Wondering how much the 645 digital format crops the fisheye. Not sure which 120 format the Arsat was originally designed for?

Thanks,
barondla

08-12-2020, 03:20 AM - 1 Like   #2
maw
Pentaxian
maw's Avatar

Join Date: Feb 2014
Location: Sassari (Italy)
Posts: 1,118
Hi barondia,

QuoteOriginally posted by barondla Quote
Wondering how much the 645 digital format crops the fisheye. Not sure which 120 format the Arsat was originally designed for?
The Arsats are (good) clones of the Kiev machines, a Soviet copy of the Hasselblad, the Arsat 120mm of which you ask has an angle of field equivalent to 31° (about 120 mm),
so a medium tele. Considering that in the 6x6 and/or 6x4.5 format, the 80mm is considered the normal equivalent of about 50mm in the 24x36 format.

Ciao Mario
08-12-2020, 03:59 AM - 2 Likes   #3
Veteran Member
johnha's Avatar

Join Date: Apr 2012
Location: Lancashire, UK
Photos: Albums
Posts: 1,155
I've tried the P6x7 35mm fish-eye on my D - the FE effect is greatly reduced - if you're careful with straight lines it might not even be obvious. The Arsat is wider, I can't comment on how much of a difference that would make.

The shot below is the P6x7 35mm FE on my D - the 100% crops were to test how badly the built-in red filter attenuated the Green & Blue channels - notice how the 'horizon' is pretty much centred to minimise the distortion of straight lines:

08-12-2020, 12:20 PM - 2 Likes   #4
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,138
645Z: 30mm ARSAT fisheye vs. 25mm DFA

These two images, taken of a neighborhood scene from a fixed tripod at f/11 and manual focus, may help show the differences in linearity and field of view. It appears that even though the 25mm DFA has a shorter focal length, the ARSAT can see a bit farther into the corners, but as expected, not quite as far in the horizontal and vertical central axes.

Attached Images
View Picture EXIF
PENTAX 645Z  Photo 
View Picture EXIF
PENTAX 645Z  Photo 
08-12-2020, 01:34 PM   #5
Site Supporter
Site Supporter




Join Date: Sep 2006
Location: midwest, United States
Photos: Gallery | Albums
Posts: 5,712
Original Poster
QuoteOriginally posted by kaseki Quote
These two images, taken of a neighborhood scene from a fixed tripod at f/11 and manual focus, may help show the differences in linearity and field of view. It appears that even though the 25mm DFA has a shorter focal length, the ARSAT can see a bit farther into the corners, but as expected, not quite as far in the horizontal and vertical central axes.
Thanks for this excellent comparison of the Arsat 30mm fisheye and 645 DFA 25mm rectilinear lenses. Really illustrates their differences.

---------- Post added 08-12-20 at 03:36 PM ----------

QuoteOriginally posted by maw Quote
Hi barondia,



The Arsats are (good) clones of the Kiev machines, a Soviet copy of the Hasselblad, the Arsat 120mm of which you ask has an angle of field equivalent to 31° (about 120 mm),
so a medium tele. Considering that in the 6x6 and/or 6x4.5 format, the 80mm is considered the normal equivalent of about 50mm in the 24x36 format.

Ciao Mario
Thanks for the information.

---------- Post added 08-12-20 at 03:44 PM ----------

QuoteOriginally posted by johnha Quote
I've tried the P6x7 35mm fish-eye on my D - the FE effect is greatly reduced - if you're careful with straight lines it might not even be obvious. The Arsat is wider, I can't comment on how much of a difference that would make.

The shot below is the P6x7 35mm FE on my D - the 100% crops were to test how badly the built-in red filter attenuated the Green & Blue channels - notice how the 'horizon' is pretty much centred to minimise the distortion of straight lines:
Interesting to see the Pentax 67 fisheye on the 645D. Looks sharp and you did a great job keeping the horizon centered to reduce the fisheye look.

Thanks everyone for posting,
barondla
08-20-2020, 01:47 PM - 1 Like   #6
Site Supporter
Site Supporter




Join Date: Feb 2018
Location: NoVA
Posts: 635
Sorry for the late hit. The Arsat is intended to be a full-frame fisheye on the 6x6 format, providing a 180-degree field of view diagonally, corner to corner.

Typically, a fisheye has an image circle of 180-degree coverage that is a little less than three times its focal length. So, a 15mm fisheye’s image circle is a hair larger than the 24x36 frame, and an 8mm fisheye fits entirely within the 24mm narrow dimension.

Thus, a 30mm fisheye covers the 6x6 frame diagonal, and a 35mm fisheye covers the 6x7 frame diagonal. The 30mm fisheye would produce a circular image on the 4x5 large-format frame, and dint think I haven’t been tempted to try and make that work.

Here’s a 30mm Arsat photo on 6x6 film, displayed without cropping:



Rick “who misssd this thread earlier” Denney
08-20-2020, 06:35 PM   #7
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,138
QuoteOriginally posted by rdenney Quote
... The 30mm fisheye would produce a circular image on the 4x5 large-format frame, and dint think I haven’t been tempted to try and make that work. ...
The hood baffle shape might make the useful image slightly truncated on the horizontal and vertical axes.

08-20-2020, 08:10 PM   #8
Site Supporter
Site Supporter




Join Date: Feb 2018
Location: NoVA
Posts: 635
Yes, but only slightly.

But the chances of me actually doing it are pretty low. Being able to do something isn’t the same thing as having a real reason to do it.

Rick “who would probably never expose a single sheet with it” Denney
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!
25mm, 35mm, 645d, 645z, arsat, arsat 30 field, camera, dfa, equivalent, fe, field, field of view, fisheye, format, lines, medium format, p6x7, post, thanks, view on pentax
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: LENS: Arsat 30mm f/3.5 (Multicoated) View Angle 180° ErinWilson Sold Items 2 11-16-2019 12:21 PM
Anyone got an Arsat 30/3.5? mattb123 Pentax Medium Format 11 03-14-2017 01:09 PM
Digital 645 questions from a digital 645 noob. texandrews Pentax Medium Format 6 05-07-2014 05:08 AM
Does the 67 to 645 adaptor change the field of view Normo Pentax Medium Format 7 09-09-2013 01:42 PM
For Sale - Sold: Arsat 30mm Fisheye lens. Pentacon 6 adapted for digital MalcolmL Sold Items 2 05-10-2013 11:10 AM



All times are GMT -7. The time now is 10:26 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