Jan 17, 2011
Works in Astronomy for Low Power ViewingPros:
Durable,Strong ConstructionCons: Comments:
Many sky observers recommend against using a correct image diagonal because it has many glass surfaces to polish/align and a linear artifact ("line") is seen when viewing - it is caused by the joint in the prisms to erect the image.
I bought this as a kind of personal astronomical experiment and find it to be very usable, especially at lower powers. This is an important caveat because this diagonal may not be for you if:
- you want to split close double stars
- you want to see many surface details on Jupiter or Mars
- you want to see many details of cracks/faults (rilles) or very small craters on Luna
- you want to see faint fuzzies at the limit of your telescope
On the other hand, this erect image diagonal is very useful to see:
- star clusters, especially open ones, and smaller asterisms
- general lunar features, such as at public outreach events or when viewing a lunar eclipse, or even during a full moon using a filter (such as Wratten 38 deep blue or Wratten 25 red, also sold by Agena) to highlight the bright cratered areas
Sometimes I get very confused as I star-hop using a simple alt-az telescope mount because most star diagonals present a topside-up but left-right reversed view and the star charts show the sky as "correct." Same thing for many (not all) maps of Luna. As a result I have to reverse the image in my head, which is not always easy for me. This diagonal keeps everything in a "normal" orientation and I can scan the heavens more easily. Many of the objects I look for require low magnification anyway, and this diagonal works well for them. I have also used it, on a whim, up to about 125x and successfully split two close moons of Jupiter and seen several of Jupiter's dark belts.
Because this diagonal uses glass prisms, it will also alter the light passing through it. For some refractors this will be a plus, because some have over-corrected spherical aberrations or insufficient chromatic correction of red light - this prism improves the image a little on my inexpensive achromat doublet. The additional glass also reduces image brightness a small amount.
Disadvantages - yes, there was image "smearing" near Jupiter, and the sky around Luna is gray from light scatter and not black. But these issues may not matter when looking a a full Luna disk that is turning red during an eclipse, or when viewing the entire solar disk in a properly filtered telescope.
This diagonal is a rather inexpensive item to add as an accessory if another star diagonal is used for those "other objects" (binary stars, etc.) mentioned above. The housing seems to be made of metal, too.
This review was provided courtesy of AgenaAstro.com
nam2525 New Member
- Skill Level
- Time with Product
Jun 30, 2007
- User Notes:
Low quality but usablePros:
Poor quality housing, poor coatings on someComments:
Don't buy one of these new!! The housing is poor quality and the coatings can be poorly applied on occasion. BUT, it does perform a basic function and usually these come free with a scope, so that is the only reason to use one. If you want a good quality 90-degree diagonal, there are plenty of other brands that offer FAR BETTER quality.
If one came with your scope, then you might use it if money is tight. Otherwise it is strongly recommended that you upgrade to a better diagonal.Sort by