Grain magnifier that can inspect outer regions?

[SeanEsopenko]

I have one of those low-cost patterson grain enlargers. The mirror is angled so that it only works in the very center of the print. Are there grain enlargers/focusing-aids that can be used on the outer regions of the print as well to check whether I'm getting diffraction issues?

[Tony Lakin]

I have one of those low-cost patterson grain enlargers. The mirror is angled so that it only works in the very center of the print. Are there grain enlargers/focusing-aids that can be used on the outer regions of the print as well to check whether I'm getting diffraction issues?

See here


http://www.bhphotovideo.com/c/product/40920-REG/Peak_130MODEL1_Critical_Enlarging_Focuser_Model.html

There was one similar marketed by Omega, both brands appear on Ebay regularly.

[Emmanuel BIGLER]

Are there grain enlargers/focusing-aids that can be used on the outer regions of the print as well to check whether I'm getting diffraction issues?

Hello from France
I've been using the French Scoponet(TM) model for years and have the same problem that you get with your Paterson(TM).
My understanding is that Peak(TM) (Japan) has a model with adjustable mirror angle capable of looking to prints off-center at a much greater distance than all other current models. the idea is that the line of sight reflected by the mirror should always point to the lens aperture (lens pupil actually) so that your eye can catch at least a few light rays through the exit eyepiece.
You'll quickly get the proper reference here from somebody who owns one.

[cyrus]

On the Peak the mirror stays put, the eyepiece rotates. The higher end model is bit pricey.

[ic-racer]

I have one of those low-cost patterson grain enlargers. The mirror is angled so that it only works in the very center of the print. Are there grain enlargers/focusing-aids that can be used on the outer regions of the print as well to check whether I'm getting diffraction issues?

Diffraction will be the same all over.

You DO want to check the corners for a myriad of other reasons. The Peak 1 is the only one I know of. It is/was also sold as an Omega Micromega (I have both and they are identical).

[Drew Wiley]

The best version was marketed as the Peak "Critical Focus Magnifier". Better optics,
tilting eyepiece, and yes, will get you a view of the corners of the field.

[Leigh]

The Peak 1 is the only one I know of. It is/was also sold as an Omega Micromega (I have both and they are identical).
I have the Micromega. It appears identical to the Peak.

Very nice item. Use in the extreme corners of the print requires a bit of contortion. :)

- Leigh

[SeanEsopenko]

Diffraction will be the same all over.

You DO want to check the corners for a myriad of other reasons. The Peak 1 is the only one I know of. It is/was also sold as an Omega Micromega (I have both and they are identical).

brain fart, yeah sorry for applying the term diffraction to outer region softness. different things, sorry bout that.

I basically want to inspect the sharpness & grain definition of the outer region before pulling a print.

[Drew Wiley]

Omega was once the marketing agent for this Peak item, hence the dual terminology.

[D. Bryant]

I have one of those low-cost patterson grain enlargers. The mirror is angled so that it only works in the very center of the print. Are there grain enlargers/focusing-aids that can be used on the outer regions of the print as well to check whether I'm getting diffraction issues?

Adobe Photoshop!:)

[aduncanson]

brain fart, yeah sorry for applying the term diffraction to outer region softness. different things, sorry bout that.

I basically want to inspect the sharpness & grain definition of the outer region before pulling a print.

Don't be so quick to apologize. While you may not have meant diffraction in your question, I think that IC was hasty in asserting that diffraction effects are uniform across the field. In fact, I believe that a comprehensive treatment of Airy disk size takes into consideration, not only the displacement of the image off of the lens' axis, but also distinguishes between the radial and tangential dimensions of the disk.

I am not sure that this variation across the field has any real practical significance for most photographic situations, but at least one well informed contributor here intimates (http://www.largeformatphotography.info/forum/showpost.php?p=584647&postcount=9) that a larger aperture will produce a sharper image at the center with wide angle lenses due to greater diffraction effects toward the edges of the image.

[ic-racer]

Don't be so quick to apologize. While you may not have meant diffraction in your question, I think that IC was hasty in asserting that diffraction effects are uniform across the field. In fact, I believe that a comprehensive treatment of Airy disk size takes into consideration, not only the displacement of the image off of the lens' axis, but also distinguishes between the radial and tangential dimensions of the disk.

I am not sure that this variation across the field has any real practical significance for most photographic situations, but at least one well informed contributor here intimates (http://www.largeformatphotography.info/forum/showpost.php?p=584647&postcount=9) that a larger aperture will produce a sharper image at the center with wide angle lenses due to greater diffraction effects toward the edges of the image.

Yes, good point, the Airy disks can flatten out on those super wides near the edges. Not something to be concerned with during enlarging as the "wide-angle" enlarging lenses are really not very wide. For example, check the MTF of the 40mm "wide-angle" Componon HM on the Schneider site ( https://www.schneideroptics.com/pdfs/photo/datasheets/apo-componon/apo-componon_28_40_2.pdf ). Both radial and tangental MTF improve at the corners with stopping down.