47 replies to this topic

[russell23]

I am starting this thread for discussion of the new APM Ultra Flat Field 65 deg eyepiece line.

 

I ordered one last Wednesday and it arrived an hour ago. Cost was $140 shipped.  Forecast looks lousy for the foreseeable future so I will report some quick late day daylight impressions with overcast skies and let others comment as they can.

 

The APM information indicates the 18mm is an 8 element in 5 groups design with 20mm of eye relief.  Markus made a point of emphasizing that this is a new design and not the same as the Flat Field design we have seen.  The caps do match the caps that come with the Orion edge on and BST flat field so I would suspect the source is the same. 

 

The eyepiece has the finish of a high quality eyepiece.  Internal blackening seems excellent with no bright rings of scattered light.  Coatings look great.  The eye lense is large.

 

I tested it in daylight and what I saw was very promising.  It does in fact appear that it will be sharp very close to the field stop- maybe a very slight falloff in the last 5% of the field of my 120mm f/7.5 ED.   Obviously a nighttime test will be more definitive, but I am hopeful. There were zero blackouts - very comfortable!

 

That is all for now except a few pictures:

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Edited by russell23, 21 November 2016 - 05:01 PM.

[joe nastasi]

Dave,

 

new eyepiece looks great! Could be just the ticket for comfortable planetary viewing with binoviewer. Eagerly awaiting your test report.

[russell23]

Dave,

 

new eyepiece looks great! Could be just the ticket for comfortable planetary viewing with binoviewer. Eagerly awaiting your test report.

I know they were designed to be sharped to the edge in pairs with the APM ED APO binoculars so I would expect they should work well with binoviewers too.

[joe nastasi]

Dave,

 

can an you tell me the diameter of the eye lens?

 

joe

[Jeff B]

Being a bino-viewer junkie, I just today ordered a pair each of the 15 & 18mm eyepieces.

 

The eye relief seems very generous really and I'm glad to hear you say the 18mm barlows well.

 

My only concern is how tight the 18mm's will be against my nose.  If need be, I'll remove the rubber eye guard like I did with my good old Smart Astronomy 27mm Flat Fields.

 

Jeff

[russell23]

Being a bino-viewer junkie, I just today ordered a pair each of the 15 & 18mm eyepieces.

 

The eye relief seems very generous really and I'm glad to hear you say the 18mm barlows well.

 

My only concern is how tight the 18mm's will be against my nose.  If need be, I'll remove the rubber eye guard like I did with my good old Smart Astronomy 27mm Flat Fields.

 

Jeff

I found no problem with the eye relief, but you can gain a little more by removing the eyecup.  I found I had plenty of room with my glasses on.  It barlows very nicely.  I tested it with the 3x TV, 2.4x Dakin, and the 2x Williams optics binoviewer Barlow operating at 1.62x.  The eye relief feels about the same as the Pentax XW.  But I cannot account for differences in facial structure.  The 18mm is a little wider than the 27mm I think.

[russell23]

Dave,

 

can an you tell me the diameter of the eye lens?

 

joe

28mm

[russell23]

I just hope when I get a chance under dark skies that there is no EOFB.  

[Jeff B]

well with a bino-viewer I've got to stick my nose between the two of them and my IPD is a bit on the narrow side.   The Denk 21 was at my limit and the old Smart 27mm close to it.

 

But I'll find out I guess.

 

Jeff

[joe nastasi]

Dave,

 

OK, thanks for that.

 

joe

[Jeff B]

Put the order in on Monday night and here they are at my home here in the state of Ohio, USA.

 

Way to go Markus!

 

Jeff

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[rockethead26]

The 18mm and 15mm are on sale at APM's Violet Day Sale. Got a pair of the 15's shipped for $220 a few minutes ago. You have to order from the Violet Day ad sale page, not from the normal eyepiece section or you will not see the sale prices. Extremely good deal.

[Jeff B]

I've posted some of my preliminary impressions in the Vendor forum:

 

http://www.cloudynig...nd-18-mm/page-2

 

Post number 34.

 

Jeff

[russell23]

I finally had some time to test the 18mm APM tonight. Targets were the Moon, M42 and M35 with my 120ED.

 

The eyepiece is sharp to the last 5% of the field with a small amount off falloff that you have to look for.  It was excellent on the moon.  Went back and forth with my 20mm XW and was really hard pressed to see any notable difference native and with barlows.  The 20mm XW was slightly more comfortable but the 18mm APM was very comfortable so the difference was more about the exceptional comfort of the XW.  I saw no ghosting or glare with the APM.  

 

I felt the stars were a little tighter in the 18mm APM when looking at M35 and M42.  It definitely has a little better snap to focus than the XW.  

 

I still haven't had a moonless clear night for good DS observing.  From what I have seen, there may be some EOFB but it takes a high transparency dark night to really see how much.  

 

More to to come in January based upon the long range forecast.

[Miranda2525]

Is there anything new about the 18mm? I am very interested in it. Thanks.

[russell23]

Is there anything new about the 18mm? I am very interested in it. Thanks.

I have not had enough good opportunities with it.   The eyepiece does have EOFB so I won't be using it for deep sky observations.  But I'm waiting for some clear skies to check it out on the Moon.

 

It is very sharp on star clusters and pretty much sharp to the edge.  The only problem I've had with it is the dang EOFB that pops up way too often in eyepieces.   What surprises me with this eyepiece is that there are almost no internal reflections.  So that blows away my hypothesis that poor blackening control of internal surfaces is the reason for EOFB.

[precaud]

 So that blows away my hypothesis that poor blackening control of internal surfaces is the reason for EOFB.

 

Don't give up on it yet. I think I may be on to something in that regard. Need to figure out how how to take photos of it (for documentation) before starting the experiment.

 

My theory is, it may in fact have to do with edge blackening; not of the side, but the lack of blackening of the chamfered edge. If that edge is visible, shine a light through the EP, and you can see a bright ring on the perimeter. If blocked by, say, a field stop, the ring is not directly visible but is still present. On smaller diameter glass, it floods the whole FOV and manifests as reduced contrast. On larger diameters, it manifests as EOFB. Like I said, just a theory, and work-in-progress, but two examples so far support it.

[Peter Besenbruch]

My theory is, it may in fact have to do with edge blackening; not of the side, but the lack of blackening of the chamfered edge. If that edge is visible, shine a light through the EP, and you can see a bright ring on the perimeter. If blocked by, say, a field stop, the ring is not directly visible but is still present. On smaller diameter glass, it floods the whole FOV and manifests as reduced contrast. On larger diameters, it manifests as EOFB. Like I said, just a theory, and work-in-progress, but two examples so far support it.

Now to figure out how to put an even magic marker line on a chamfered lens. I would not look forward to that.

[russell23]

 

 So that blows away my hypothesis that poor blackening control of internal surfaces is the reason for EOFB.

 

Don't give up on it yet. I think I may be on to something in that regard. Need to figure out how how to take photos of it (for documentation) before starting the experiment.

 

My theory is, it may in fact have to do with edge blackening; not of the side, but the lack of blackening of the chamfered edge. If that edge is visible, shine a light through the EP, and you can see a bright ring on the perimeter. If blocked by, say, a field stop, the ring is not directly visible but is still present. On smaller diameter glass, it floods the whole FOV and manifests as reduced contrast. On larger diameters, it manifests as EOFB. Like I said, just a theory, and work-in-progress, but two examples so far support it.

 

I think you are right.  When I tried to eliminate the EOFB in the13mm Olivon 70 the last step I had to try was blackening the chamfered edge of the eye lense.  I managed to get the lenses jammed before I could try that and never had a chance to test it ... but the frosted look of EOFB makes me think that light seeping through the chamfered edges could explain EOFB.

[precaud]

Now to figure out how to put an even magic marker line on a chamfered lens. I would not look forward to that.

Challenging, indeed...

 

... I am seeing an appropriately-sized rotating platter with vacuum hold-down... foot-operated speed control... an adjustable handrest attached... add intense local lighting and a pair of magnifying eyeglasses and yes, that would do nicely!

 

Oh, I forgot, someone standing over you from behind as you work, gently rubbing your shoulders...

Edited by precaud, 06 January 2017 - 03:39 PM.

[APO1]

Please excuse my ignorance, but what is EOFB?

[Kent10]

EOFB = Edge of Field Brightening

[russell23]

I had SW120ED out tonight for a look at the Moon.   Temperature is <10 deg F so I only stayed out for ~ 1 1/2 hours.  But in that time I thought the 18mm APM did an excellent job on the Moon.  It was very sharp with a very stable exit pupil. 

[Miranda2525]

I had SW120ED out tonight for a look at the Moon.   Temperature is <10 deg F so I only stayed out for ~ 1 1/2 hours.  But in that time I thought the 18mm APM did an excellent job on the Moon.  It was very sharp with a very stable exit pupil. 

Thank you sir. I am quite interested in the 18mm APM. Where did you buy yours from if you don't mind me asking?

Edited by Miranda2525, 07 January 2017 - 02:03 AM.

[russell23]

 

I had SW120ED out tonight for a look at the Moon.   Temperature is <10 deg F so I only stayed out for ~ 1 1/2 hours.  But in that time I thought the 18mm APM did an excellent job on the Moon.  It was very sharp with a very stable exit pupil. 

Thank you sir. I am quite interested in the 18mm APM. Where did you buy yours from if you don't mind me asking?

 

I responded to an ad Markus Ludes posted on Astromart.  They get back to you with a billing statement and then you can pay them by whatever method you are using.