Diagonals

[John]

I've compared my Amici roof prism diagonals with my standard diagonals and I can't see any denigration of image or other problems. I suppose it depends on your scope or something. Admittedly I want an Everbrite, but for lunar/planetary particularly I can't discern any difference with an erecting prism, apart from the image being corrected. I think erecting prisms were poor quality at one time and gained a bad reputation. That doesn't seem to apply in the 21st century.

I've tried a few and found that they all introduced some sort of unwanted issues when used for astronomical purposes. I've still got a couple knocking around in a drawer somewhere.

This reviewer found similar issues with a rather nicely executed 2" William Optics one:

http://www.cloudynights.com/page/articles/cat/user-reviews/accessories/star-diagonals/william-optics-45-deg-erecting-prism-r1383

Here is a more recent thread on the topic from the "Cloudynights" forum:

http://www.cloudynights.com/topic/464304-correct-image-diagonals/

I'd really not reccommend an fully corrected prism for astronomy apart from for use in a RACI finder.

[LukeSkywatcher]

The beauty of imaging is that you can let the camera roll overnight and subtract rubbish frames/exposures the next day. Visual observers have to sit and wait for breaks in the cloud.

[Mak the Night]

I've tried a few and found that they all introduced some sort of unwanted issues when used for astronomical purposes. I've still got a couple knocking around in a drawer somewhere.

This reviewer found similar issues with a rather nicely executed 2" William Optics one:

http://www.cloudynights.com/page/articles/cat/user-reviews/accessories/star-diagonals/william-optics-45-deg-erecting-prism-r1383

Here is a more recent thread on the topic from the "Cloudynights" forum:

http://www.cloudynights.com/topic/464304-correct-image-diagonals/

I'd really not reccommend an fully corrected prism for astronomy apart from for use in a RACI finder.

I know the 45° roof prism diagonals have several astronomical issues, light path problems are one, I believe, but I think the 90° diagonals fare better and are relatively fine for certain targets. It's been my experience, with bright largish objects such as planets, and particularly the Moon, even at high magnifications. Although I do use them with a f/12.7 scope, which may contribute to this. I've directly compared them with my standard diagonals (Celestron, Sky-Watcher, TS Optics) on non-planetary objects at comparatively low magnifications and I also can't see any differences. I may notice it with splitting binaries if I knew what to look for but I just don't see anything amiss at present. Although even then, I normally don't go higher than 130x-180x. When Telescope House decide to restock I will order a TeleVue Everbrite anyway. I have a feeling I'll need it for many DSO's when I finally get a 9.25" SCT. My standard Celestron diagonal is quite capable but I'd like a decent mirror prism. Diagonals are a lot like eyepieces to me, I'll swap and change depending on what I'm viewing.

[Mak the Night]

Talking about stuff knocking about in drawers somewhere.

I acquired this William Optics deluxe 45° 1.25" erecting prism from FLO a while ago. Admittedly it has been stuck in a drawer for quite a long time. I originally bought it as I was experimenting with adjusting the height  of my Mak tripod and when it was set very high (EQ mount) I thought this may be an advantage. With my disability, standing and sitting are fine, unfortunately anything inbetween is difficult or nigh on impossible. I was viewing planets/Moon rising in the east/south east and sometimes Jupiter and Venus setting in the west. 

Eventually I developed a regime where I could sit for most observing essentially precluding the use of a 45° diagonal. Funny thing is, even with a 2x Barlow (usually a shorty Celestron Omni) in combination with 12, 13, 15 and 17mm Plossls I couldn't detect any noticeable visual distortions, reflections or image problems. 

I'll keep it as it may come in useful for daylight observing with the Mak as a spotting scope one day. I can envisage it being used to observe early morning rising planets with a grab'n'go tripod one day. Or pigeons. 

[John]

I found the roof prism design (in 45 or 90 degrees) used to deliver a fully corrected image can produce a thin streak or line of light either side of a bright star, rather like a diffraction spike in a newtonian. You can apparently get them where the prisms are ground to very high quality where the effect is more or less elminated but those have high price tags.

To me the reversal of left and right in astro viewing is not an issue so I can't see the point of limiting my choice of diagonal to relatively few fully RACI ones when there is a much wider range of ones offering the standard view available.

My current diagonals are 2" TV Everbrights which are pretty nice. I believe that diagonals employing single high quality prisms can be even better performance-wise, especially on the planets, if one is after every possible performance advantage. Bill Paolini's diagonal review is interesting:

http://www.cloudynights.com/page/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

[Mak the Night]

I found the roof prism design (in 45 or 90 degrees) used to deliver a fully corrected image can produce a thin streak or line of light either side of a bright star, rather like a diffraction spike in a newtonian. You can apparently get them where the prisms are ground to very high quality where the effect is more or less elminated but those have high price tags.

To me the reversal of left and right in astro viewing is not an issue so I can't see the point of limiting my choice of diagonal to relatively few fully RACI ones when there is a much wider range of ones offering the standard view available.

My current diagonals are 2" TV Everbrights which are pretty nice. I believe that diagonals employing single high quality prisms can be even better performance-wise, especially on the planets, if one is after every possible performance advantage. Bill Paolini's diagonal review is interesting:

http://www.cloudynights.com/page/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

I may have seen this streak and not properly noticed it, or maybe it's just not so noticeable on my little Mak. If I'm not using the bog standard Celestron diagonal, and have an erecting diagonal in the telescope, when I'm possibly star hopping inbetween lunar and planetary viewing, I'm probably observing at quite a low power (often TV 32mm Plossl giving 41x). Also, my dominant eye (right side) suffered with some muscle control after my brain bleeds. This made normal (involuntary) blinking difficult and the eye had a tendency to dry more than the other. Although I suffered no loss of vision and had good eyesight previously. So this may also be a factor. I read Paolini's review a while ago and it is very interesting. I have heard that about high quality prism diagonals too, although I'm pretty set on an Everbrite. They look beautifully made.

[brrttpaul]

So I was just wondering here atm I can see through the viewfinder of my nikon attached to the scope if i bought a prism/diag what would the diference be in terms of clarity? also I have some eyepieces that I have never used (super wides, barlows, think they range from 7 to 25mm  would I need new eyepieces for terrestrial viewing?

[Pig]

Paul,

Your selection will be fine, just simply experiment with them to determine the best eyepieces for close ups and distant views . I have found a zoom eyepiece to be very useful for daytime use. Quality comes into play as with any hobby.