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Old 15-06-2019, 02:30 AM
Renato1 (Renato)
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Join Date: Mar 2014
Location: Frankston South
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Quote:
Originally Posted by Outcast View Post
Sirius 38mm... it's clear & gives a full fov to an 8" SCT with 2" visual back & it was relatively inexpensive at $159 (from memory), it's no UWA or ES but, it does it's job & the views are pleasant enough (well, to my eye)... I can't say it's sharp to the edge or anything (I seriously doubt that it is) because I don't really do my viewing out to the edge so much anyways.. well except on big nebs... & nebulosity doesn't really look 'sharp' as such anyways...

Will be crap in a fast Newt though...

Furthest I pushed my Meade APO when I owned it was 178x, with my 6.7 UWA coupled with powermate... I thought the view was superb but, that's only just over theoretical max of 160x....

I've got some shorter focal length EP's now; 6mm Fujiyama ortho & an el cheapo Celestron 4.7mm kit EP I got in a bundle of other stuff...

The ortho's are exceedingly good planetary EPs but... nil, nada... zero eye relief, particularly down at 6mm.. I'll bung it in my powermate one night.. that'll give me 200x.. see how it goes...

The celestron with the powermate would technically give me 300x but, I haven't actually used that EP in anything since I got it so.. I'm not even sure if it will be any good at it's native FL to be honest...

I don't own anything decent below 6mm, with the 2.5x powermate I don't feel I really need to...

I've read a lot of different opinions on the Meade UWA's some good, some not so... I do believe the 6.7mm is one of the originals that were actually made by the chap that then formed ES.. I believe the later ones I've got are possibly made at a different company later on... with maybe a slight design change; I'm not really sure on that... as you probably know, it's all but, impossible to get definitive design info on pretty much all EP's.... the manufacturers rarely if ever state their exact design... All I know is that I fell in love with my original 6.7mm & the rest that I acquired from the US late last year (new... sadly not made anymore, so lucky) definitely do not disappoint...

Cheers
That theoretical maximum of 160X equates to 50X per inch, which is most applicable to Newtonian telescopes. But refractors can go higher than that if they are high quality and the atmosphere is good, because they have better contrast and no obstruction.

Keep in mind that there are two types of visual recreational astromers in the world. Those who see some distortion at the edge of the field and don't mind it, or don't even notice it - and those who see it and it drives them nuts. The chap who sold me my first SCT was like the latter type, whereas I was happy using a 20mm Erfle to view the 1000 or so DSOs I then saw through that SCT. To my mind, if I saw more good quality field of view in the Erfle than I'd see in an equivalent 20mm plossl - I was ahead - despite the edge distortion.

Don't be too sure that the Sirius will be rubbish in your new dob. I've got a 40mm Konig with 60 degree field which I used to take for a spin through starfields in my 14.5" F/4.5 dob. That's an 8.8mm exit pupil - and I'd read articles saying that was a waste of aperture, and that it wouldn't work because the secondary mirror would show up in the stars. That was all rubbish, the view was fine (apart from some distortion at the edges). Plus, as a bonus, I found that I could tilt my eye and get rid of my eye's astigmatism without blanking out part of the image.
Regards,
Renato
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