Graflex.org Forum Index Graflex.org
Get help with your Graflex questions here
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Lenses for the Crown Graphic
Goto page Previous  1, 2, 3
 
Post new topic   Reply to topic    Graflex.org Forum Index -> Lenses Help
View previous topic :: View next topic  
Author Message
troublemaker



Joined: 24 Nov 2003
Posts: 715
Location: So Cal

PostPosted: Sun Nov 30, 2008 2:09 am    Post subject: Reply with quote

Where did I get the idea that tessars are a very old design with an average angle of 62 degrees? Seems towork for me up and down the focal lengths.
The 75mm tessars covers 6x6 and that's it, while the 101 and 105 tessars cover 6x9 very nicely even with small movements. The 127 much the same with the obsolete 3x4, but will cover 4x5 stopped down, and the 135 covers easily 4x5 and allows slight movements stopped down. At 55 degrees this would not be the case.
Am I correct in thinking this? Not being a lens guru, I claim no special knowledge so perhaps the lens wizard will check the magic book and report...
Back to top
View user's profile Send private message
Bruce Curtis



Joined: 26 Nov 2008
Posts: 5
Location: Jeffersonville, Vermont

PostPosted: Sun Nov 30, 2008 3:02 am    Post subject: Reply with quote

Hi Speedtrials, I have never been able to find much info on Wollensak Optars, but I did find the info that they were a Tessar-type that had an angle of coverage of 55 degrees that works out to 140mm image circle. This tidbit about their design was found on a Photo.net page while I was looking for some other unrelated info My own experience and what I have read from legitimate sources about press photography with Graphics using semi-short lenses like 127's and 135 optars, was that they needed the extra room incase they didn't frame properly in the heat of battle, and they weren't concerned with the fall off in the corners because they would usually crop the negative most of the time anyway. I'm not knocking your 135 Optar. When I used to do shows in the 80's and 90's other dealers wouldn't touch 135 Optars unless they were freebes. Never had a problem selling 2.8 Xenotars though.
_________________
Bruce Curtis
Back to top
View user's profile Send private message
Dan Fromm



Joined: 14 May 2001
Posts: 1888
Location: New Jersey

PostPosted: Sun Nov 30, 2008 10:49 am    Post subject: Reply with quote

troublemaker wrote:
Where did I get the idea that tessars are a very old design with an average angle of 62 degrees? Seems towork for me up and down the focal lengths.
The 75mm tessars covers 6x6 and that's it, while the 101 and 105 tessars cover 6x9 very nicely even with small movements. The 127 much the same with the obsolete 3x4, but will cover 4x5 stopped down, and the 135 covers easily 4x5 and allows slight movements stopped down. At 55 degrees this would not be the case.
Am I correct in thinking this? Not being a lens guru, I claim no special knowledge so perhaps the lens wizard will check the magic book and report...
TM, there are two things going on.

There are tessars and there are tessars. If the VM is to be believed, f/6.3 tessars cover 70 degrees. Faster tessars have less coverage, and the faster the lens the smaller the angle/circle covered.

There's also disagreement about what "covers" means. Some interpret it as "illuminates." Others as "puts good image in the corners." And there's disagreement about what "good image" means.

Schneider used to publish MTF curves for their lenses. I've just looked, can't find 'em now. But I have looked at their curves for Xenars and have noticed that those lenses MTF curves were nearly vertical, i.e., falling fast, towards the edge of claimed coverage. In the propaganda I found today, Schneider claims that Xenars cover 62 degrees. Maybe, but IIRC 62 degrees is roughly where the MTF (contrast at fairly low resolution) went to zero.

Funny you should think that the 101/4.5 Ektar covers 2x3 well. I like my 101 Ektar, think it is a fine and very useful lens. But at f/16 mine puts a much softer image in the corners than is the center. So I think mine is a bit iffy on 2x3.

Whether softness in the corners matters depends on what the photographer is trying to accomplish. If what's in the corners isn't essential to making the image work, who cares about the corners? And if the negative isn't going to be enlarged much, corners that are softer than the center can be tolerated.

Cheers,

Dan

I've had to reconsider my ideas about what's sharp enough. I got a Perkeo II last year, haven't got a really sharp shot with it yet, even when shooting from tripod. I don't think the 80/3.5 Color-Skopar is a wonderful lens. But I have got some shots that, when printed 8x10, work fairly well; even though they won't stand close scrutiny, composition and color save them.
Back to top
View user's profile Send private message
troublemaker



Joined: 24 Nov 2003
Posts: 715
Location: So Cal

PostPosted: Sun Nov 30, 2008 5:29 pm    Post subject: Reply with quote

Thanks Dan,
I went and found the Schneider Vintage lens pages and bookmarked.
Yeah they suggest 61 to 62 degrees for thier faster series of Xenars, but that at f16 which I shoot at a lot. I'm not so technical as some, thus I tend to base my shallow assumptions on experience with useable and pleasing images. The 101mm I was thinking of is the Optar/Raptar, and 105 Xenar.
When I've shot the 135 in field with Provia the corners were fine, but at the smaller apertures I use for landscape. On the other hand I made a comparison wide open at f4.7 and f16 and noticed a big difference on the one I checked out. Wide open was much softer and very nice for a female portrait. I wasn't so much concerned with the corners when I did that, but I imagine the fall off was severe at the edges. I certainly wouldn't suggest it for architectural 4x5 work.
Back to top
View user's profile Send private message
Dan Fromm



Joined: 14 May 2001
Posts: 1888
Location: New Jersey

PostPosted: Sun Nov 30, 2008 5:46 pm    Post subject: Reply with quote

troublemaker wrote:
I'm not so technical as some, thus I tend to base my shallow assumptions on experience with useable and pleasing images.


Wrangling about words and calculations is great fun, but in the end what matters is that the images please.

Cheers,

Dan
Back to top
View user's profile Send private message
jan normandale



Joined: 13 Nov 2007
Posts: 30
Location: Toronto Canada

PostPosted: Mon Dec 01, 2008 2:10 am    Post subject: Reply with quote

Dan Fromm wrote:
troublemaker wrote:
I'm not so technical as some, thus I tend to base my shallow assumptions on experience with useable and pleasing images.


Wrangling about words and calculations is great fun, but in the end what matters is that the images please.

Cheers,

Dan


That's what I think too. TTYL, Jan
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Graflex.org Forum Index -> Lenses Help All times are GMT
Goto page Previous  1, 2, 3
Page 3 of 3

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group