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eye placement apparently changed

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I meant to mention this in my brief report the other night but forgot so here goes.

My new scope is 350/1700 F4.8 newtonian dob.  The eye placement appears to have altered when using my Nikon eyepieces, before I could really sink my eyeball into the cup to get that drifting into space experience. Now if I try doing this I experience quite bad kidney beaning and the eye relief appears to have increased. I can adapt to this but it just feels weird at the minute, thinking maybe eyepiece cup extender from TV might help although will try without first.

I don't know if anyone can shed light on this and I don't know if this is relevant but the old scope was 250/1200 F4.7 newt. 

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  1. Are you using the same coma corrector in both?  I have certain eyepieces that exhibit a fuzzy field stop without a CC, and a sharp one with one.  I've never noticed SAEP becoming more or less pronounced with or without a CC.
  2. Is this the only scope that causes the Nikons to kidney bean?  It is very odd indeed.  I've not heard of this issue before.
  3. Do any other eyepieces in your collection kidney bean under the same conditions?
  4. Do the Nikons kidney bean with or without the EiCs installed?

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Hi Louis, in anser to your follow up queries I am not using a CC, didn't use it with the nikons before with my other dob. 

I only use the nikons in the dob, I have more glass for my other ota's.

I also used a 30mm antares eyepiece the other night and it was a pleasure to use.

Not tried with the EIC yet.

I only did a little viewing the other night, but there was definately a change to my viewing experience. It seems as though the sweet spot has pushed back a few MM but I can't confirm this to be the case as yet. It being the first time i used the scope there was a lot going on, and I think I got a little hung up with the DSC when really optics should have been the first thing to get to grips with.

More practice tomorrow night (weather permitting) and I shall see how I get on. I also have a dioptrix which I can play around with to see how that works with the 17mm version. I don't need it with the 12.5mm version.

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I can't tell you why what you are experiencing happened, but it's not in the eyepieces.

Both scopes have nearly identical focal ratios, so the angle of light entering the bottom did not change.

Likewise, the exit pupils did not change noticeably, either.

So that leaves the observer.

It's highly likely that if your other eyepieces have less eye relief that you are just reacting to the eye relief in the Nikons.

When I converted from Nagler Type 6 eyepieces with 12mm eye reliefs to Ethos eyepieces with 15mm of eye relief, at first I continually drifted inside the exit pupil and got blackouts.

After a while, I adapted to the 3mm longer eye relief and when I went back to the Naglers, I found them cramped in eye relief.

So if you stayed away from the scope a while, or used other eyepieces for a while, it's entirely possible you'll have to readapt to the eye relief.

The eyeguard extender from TeleVue removes over 1/2 of the eye relief of the Nikon, so unless you like to get your eye closer than the length of your eyelashes, I wouldn't recommend it.

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I know this sounds overly simplistic, but being a taller scope, is it possible you are holding your head at a slightly different angle than before? Or maybe the focuser is mounted at a slight angle in relation to the secondary and needs some adjustments there? Just trying to eliminate simple things first... 

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Thanks Don and Ships, two interesting ideas on why things appear to have changed.

I was using the Nikons in the previous dob scope only 2 weeks since with the Nikons, I purposely got it out to try to get a strong memory of what I had before changing to the new scope. Therefore I am not convinced with your idea that I have lost my memory of eye placement of the eyepieces, although i am not totally discounting it. 

I am a leaning more to Ships idea that the whole setup is different in dimension, angles of focuser and placement of your head when using it. Actually this does blend in with Don's explanation as the two are kind of the same, just explained differently. Although in the former it's not forgotten eye placement, just totally new.

Wittering a little now but the old 10" dob I could easily move my head into the same position each time I used it, I think with the T350 I was struggling just a little with eye placement at the focuser. Ah well first timer out and all that.

I think that makes sense now,  cheers guys.


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