Binoviewer for Maks?
Posted 25 April 2013 - 07:12 AM
I am looking for the convenience of a Binoviewer for my new Mak 127 (SLT Celestron) for planetary and lunar observations..maybe for DSO?
Which is your opinion , is a good accessorie for a Mak ?
If so, how much magnification with binow.?
Posted 25 April 2013 - 07:50 AM
Meade 2120 Premier 10" LX200 Classic
Celestron Nexstar 8SE
Meade 90mm f/8.8 Refractor
Celestron 90mm mak
Celestron CG5 Advanced mount
Celestron Bino Viewer
Canon T4I for Astro and Terrestrial imaging
Posted 25 April 2013 - 08:22 AM
There are three issues.
First, the binoviewers themselves will dim the view. If you were starting with more apeture or you could go down some in magnification and recover some of the brightness simpy by rasing the exit pupil size.
The issue with this though is that the binoviewers are going to add a lot of back focus, and in a moving mirror scope, this means that the focal lenght will increase. Your 1500mm scope will become something like a 1700mm scope, and this will mean that even a 25mm plossl pair will be giving 68x or a 1.75mm exit pupil. This is a pretty small exit pupil for much deep sky work, and will limit you to a farily small true field, so larger clusters will over-run the field.
Finally this.. I don't know if it is the case with your scope or not, but many of these 5" MCTs are only working at about 120mm. With the binovewer though, you may find that the apeture is furter reduced, perhaps down to 110mm, depending on the exact configuration.
I think binoviewrs make more sense for planets in small scopes but not for deep sky in an instument that starts with such a long focal length.
If you decide to do it though, my advice is very strong and it is to use the Baader Maxbright Binoviewr with the Baader T2 Prism diagonal. This will give you the shortest possible light path, and also has slighly larger prisms than some less expensive models.
Keeping the light path as short as possible is the key to getting the best performance out of an MCT or SCT with moving mirrors.
I love binoviewrs, and I use them on my C5 all the time, but I have a very short light path, and my prisms allow for very low power eyepeices with the full field (40mm Plossls) so I can get a decent size exit pupil.
If you do it though, I can't tell you how strong muy recommendation is to go with the Maxbrights/T2 Prism. They will cost you more but the quality is excellent and they will give you the best chance possible of being successful at using the BVs for DSOs. Using these in your scope, you will get a bigger, and brighter true field.
Hope this is helpful, and good luck with your decision.
Posted 25 April 2013 - 09:05 AM
Otherwise? The image in a binoviewer may be dimmer due to loss of light in the prisms/beam splitter, but that is not how the eye sees it. I once did a binoviewer/Cyclops style shootout from the dark skies of the Chiefland Astronomy Village with my C11. Object after (deep sky) object, I could always make out more detail with the Denk. Period. Sometimes the image looked dimmer, but usually not. Using two eyes seemed to make it appear at least as bright.
My experience has also been that you need a good/optimized binoviewer to make deep sky binoviewing the experience it can be: Denkmeier or Earthwin, that is.
Posted 25 April 2013 - 02:13 PM
Eddgie, i've actually been looking into the Maxbright.
Posted 26 April 2013 - 07:52 AM
Sadly, in many scopes, this may be the case unless great care is taken with the configuration.
For example, my C14 works fine with the Mark Vs, but with the Denkmeier/Supersystem, the apeture was cut down from 14" to about 13.3". This does not sound like much, but coupled with the binoviewer, the view seemed dim to me.
When I went to the Maxbright, I felt the view was brighter.
In the EdgeHD 8" though, the situation was much much worse. The apeture of the EdgeHD when using the 2" based powerswitch system was reduced to about 6.8" or so (calculated) and with the reducer, about 6".
Even with the Baader Clicklock (about 40mm of light path) the T2 Prism (about 38mm of light path) and the Mark V (123mm of light path), the EdgeHD 8" is only working at 7.5mm. This does not sould like much, but it is about a 15% change in brightness, and the central obstruction size goes up in percentage.
I have since gone to the Baader 15mm SCT adapter, so have shaved about 22mm more off the light path, but the aperture is only 7.7 inches.
I have been posting all of this in the Binoviewer forum, and my advice would be to ask there.
I still like them for planets, but I do almost all of my planetary observing with my C14, so the fact that the EdgeHD 8" and the C5 both loose apeture is not a big issue to me.
But once again, for deep sky, you are loosing some brightness (read Edz's contributions at the top of the Binoviwer forum.. He has great links and summaries about binoviwer dimming there) from the binoviewers, and when you couple the potential for apeture loss, it means that there is some risk of having a system that is sub optinal to the point of risking your satisfaction with the purchase.
I would post in the Binoviear forum and ask if anyone has measured the configuration you are contemplating before jumping in.
If you decide to go though, the Baader 15mm SCT to T2 Adapter, Baader standard T2 Prism, and Maxbright is going to give you the best chance of keeping all of your aperture (or as much as possible) and the brigtest image possible.
I loved the Maxbrights and the Baader system approach. I since went to the Mark V, but the view is not meaningfully better. The main reason I went to the Mark V was for the extra true field. It is an expensve way to get it, but for me the price was not an issue.
I would try to find the answer though, to the quesiton about potential aperture loss.
Maybe it doesn't make any difference to you though, and if not, then go for it.
Posted 26 April 2013 - 08:11 AM
Posted 26 April 2013 - 08:17 AM
Posted 26 April 2013 - 11:26 AM
For example if you had an aftermarket focuser and a 2" diagonal, then put your binoviewer on, you might run out of mirror travel.
I would always advise a 1.25" diagonal for these kinds of scopes because they light path is much shorter than with a 2" diagonal, so the focal length will be much shorter and you will get a brighter image this way. And with a 1.25" diagonal, I think that you will likely reach focus with no problem.
A GPC might be a good idea if your scope is loosing aperture because of binoviewrs.
For planetary viewing, a powerful GPC (or Barlow) will allow you to move the mirror back, which can help you re-gain lost aperture.
For general viewing, I guess a little aperture loss is not the end of the world, but for planets, I would try hard to keep as much aperture as possible, and a powerful GPC or Barow might even get you full aperture depending on the configuration.
But you will likely be able to reach focus without it.
Posted 26 April 2013 - 11:27 AM