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2" vs. 1.25"


Tommohawk

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Hi All. Have had lots of help from this forrum, so am hoping someone can advise me on this. Am rank novice - have recently aquired Skywatcher explorer 150p, and want to view and hopefully image DSOs and planets if possible. I realise there will be compromises, but would like to make a start somewhere!

I have the loan of a Nikon 3200 body, so intend to do some prime focus imaging. Probably direct for DSOs, and with Barlow for planets. Hopefully that sounds sensible.

So far I have just the standard 10mm 25mm EPs and x2 Barlow. So before I buy the adaptor, and probably an EP or two, I'm wondering if theres anythng to be gained by going to 2" set-up? That is, 2" adapter, 2" Barlow, and 2" eyepieces?

Is there any advantage from the imaging point of view? I'm guessing not..? Maybe mechanically better support for the camera?

For viewing without camera, 2" EP would presumably give better field, and may be better as I'm a spec wearer. But would it limit the mag? I'm guessing bigger diameter would mean shorter focus may be a problem? If using the 2" eyepiece with Barlow, does the 2" Barlow offer any advantage over 1.25"? Again, I guess maybe not?

Oh and whilst I think of it, I think the biggest compromise for me will be with planets - not enough magnification I suspect. So would I be better ditching the Barlow in favour of EP projection.... and if so, again should I go 2".

So many questions...!!

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I've yet to test this as awaiting adaptor but I think vignetting will be a problem when photographing through 1.25 eyepieces. 

Focusing on 150p may also be an issue. I am sure  other members will be able to expand on this.

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You don't use eyepieces for prime focus imaging. You simply fit the camera with a 2" nosepiece instread of a lens, straight into the focuser, so the camera sensor sits at the focal plane of the telescope. Certainly Canon cameras will come to focus with a newer (last 2-3 years) 150P. If the backfocus distance of the Nikon is similar you should be fine. For planets, you definitely need a barlow but you would probably do better with a web cam or use video mode on your camera, if it does video. Doesn't make any difference if it is a 2" or 1.25" barlow, you just need the correct nosepiece for it. The SkyWatcher 2x deluxe barlow has a T-thread, so ou can fit a T-ring and attach directly to your camera. It's not the best barlow but okay to give you taster.

For visual use, in focal lengths longer than about 20mm, 2" eyepieces can show a wider field of view than 1.25" eyepieces of the same focal length. Below that focal length, they can both show the same field so no advantage, in fact 1.25" would likely be lighter and cheaper. Like many people, I have one low power super wide angle 2" eyepiece, 28mm in my case, all my others from 21mm down to 3.5mm are 1.25" but they all show 68-70° apparent fields. (The circle you look through seems the size, just the magnification changes).

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Hi Dave, and thanks for reply. I think I read that focussing on the new newer 2" 150P is not a problem. Hadnt though about vignetting issue with EP projection - good point. do you think a 2" would resolve that?

I have read that you need 2" eyepiece/holder for photographing to avoid vignetting but as I said have not tried yet as do not have appropriate adaptor to attach camera to eyepiece. I have tried hand holding my camera body in front of eyepiece for close up of moon and Jupiter pics and there is some darkening at the edges, whether this is vignetting or just because I was not central I am not sure.  Think you will need your 10mm eyepiece + barlow for any detail in planets but these will be 1.25". Moon is good first target should be fine with camera body + t-ring + adaptor with or without barlow. Again make sure you can focus before spending money.

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You don't use eyepieces for prime focus imaging.

Yes, I did realise this. I just wondered that if I was going to buy new EPs for general viewing, would 2" be better.

 The SkyWatcher 2x deluxe barlow has a T-thread, so ou can fit a T-ring and attach directly to your camera. It's not the best barlow but okay to give you taster.

Ahhh - I didnt realise that - the fine external 42mm thread screws into the adaptor - thats handy. And have just realised this particular barlow splits into 3 sections, so can take off the Barlow and use as 1.25 camera adaptor direct. Excellent. When I intially split this, the barlow came off with the centre section, and I couldnt see how it would work. Took a while to figure you can remove just the last section with the Barlow, and leave the 1.25 tube.

For visual use, in focal lengths longer than about 20mm, 2" eyepieces can show a wider field of view than 1.25" eyepieces of the same focal length. Below that focal length, they can both show the same field so no advantage, in fact 1.25" would likely be lighter and cheaper. Like many people, I have one low power super wide angle 2" eyepiece, 28mm in my case, all my others from 21mm down to 3.5mm are 1.25" but they all show 68-70° apparent fields. (The circle you look through seems the size, just the magnification changes).

OK see you point. Most of the detail viewing work would be with shorter lens, so no FOV benefit.

But I wonder would there be any better "relief" value, given I'm a spec wearer?

Again make sure you can focus before spending money.

Like your thinking!

Well, it looks like all I need is a Nikon T ring to get started. So willl get that, use direct with adaptor from the Barlow for DSOs, add the barlow for planets and see whee I go from there.

I saw a fabulous M31 image here shot with a 130P and if I can get even close to that I'll be thrilled.

I get the impression that EP projection will give more mag for planets than barlow, so maybe will try that also. Any thought on what hardware I should get for that?

Many thanks, Tom

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But I wonder would there be any better "relief" value, given I'm a spec wearer?

Eyerelief is dependant on the design of the particular eyepiece and not related to barrel size. Actually most Ultrawide/Hyperwide eyepieces have fairly tight eyerelief in the shorter focal lengths. Not uncomfortable but too tight to use with glasses. I also wear glasses to observe, so use EP's with 20mm eyerelief, mainly Pentax XW's, but my 2" is an Explore Scientific 28mm 68º, and I also have a Baader Hyperion 3.5mm but this doesn't get much use.

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You will need an adaptor to attach camera body to eyepiece and possibly??? a small extension tube. The type, design of this will depend on your eyepiece. I have a BAADER Hyperion which has a built in thread M43 undermeath the rubber eyecup and I have ordered a M43/T2 adaptor which will connect camera body to it.

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Thanks for advice. I think I have it sorted. I'm going to order Nikon ring, and then this.

The ring will connect to this for planetary work using EP projection method, or I can just use the ring plus the first outer section which has a 51mm diameter to connect to the 2" telescope focuser for prime focus. Not sure its meant for this, but its 2" so should work.

Also of course I can then connect the ring to the barlow and see how that works. Should give me a good few options to be gloing on with. Hopefully nobody will point out some hideous flaw in my plan!

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  • 4 months later...

You will need an adaptor to attach camera body to eyepiece and possibly??? a small extension tube. The type, design of this will depend on your eyepiece. I have a BAADER Hyperion which has a built in thread M43 undermeath the rubber eyecup and I have ordered a M43/T2 adaptor which will connect camera body to it.

I have a 10mm Baader Hyperion eyepiece too - are you suggesting that a DSLR can be connected through the eyepiece, presumably providing additional magnification, so (for example) you could photograph a planet through it and get something better than a dot? If so, that would be worth me trying, so interested to know... I already have the relevant adaptor and T-ring to connect my (Pentax) to my scope(s). Cheers!

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