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Observing Report using Binoviewer Ready 130mm Refractor

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#1 Eddgie

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Posted 11 January 2024 - 10:47 AM

It has been a while since I have written any kind of observing report and while this could just as easily been posted to the refractor forum, the content here is geared not only at the observing I did, but also on the befits of a scope properly set up to use binoviewers.

 

The scope is a Photoline 130mm f/7 Apo with FPL-53 and likely using BSL7 or  N-BK7. This combination will yield a polychromatic Strehl of .973739, which is to say that the instrument is essentially completely color free on even the brightest stars. This means that any color seen when using binoviewers if from the binoviewer itself and not the telescope.  

 

The first thing to point out is that when you use a binoviewer ready telescope, you greatly shorten the physical length of the telescope. When you use the same size telescope in a normal mono-view configuration, it will be approximately 90mm longer.  This does not sound like much, but it could mean the difference between sitting on the ground to view at zenith, and having to stand when viewing near the horizon because your observer chair won't go low enough for zenith or high enough to sit comfortably when viewing low in the sky. The reason for this second one is simply due to the fact that when you fold the light path 90 degrees, you have now raised the eyepiece height maybe 100mm above what it would be if you were using a conventional eyepiece. You can solve the sitting on the ground problem by using a tall pier, but this makes the standing when viewing lower in the sky even less ergonomic. 

 

In my case, I am using a T90 Tripod with the iOptron mini-pier (one day I hope to get the Avalon pier as I think it would be more stable). Using a Semi-Pier will almost always have the cost of reducing stability, but it is often necessary to avoid having the telescope hit the tripod legs. A true pier mount like the iOptron Tri Pier, at tripod I have owned, will solve this and provide excellent stability (I have owned one of these) but at the cost of some extra weight. 

 

Together, these things mean that the shorter tube makes the scope more comfortable to use when viewing low and high and makes for less issue with the telescope hitting the legs

 

It is hard to say that the shorter tube improves the stability because while a full lenght mono-view setup will have a longer moment, it is also much lighter out there at the back end. Even with the weight of the heavy triplet objective, given the weight of the BV and eyepieces, you add enough weight that you kind of counteract for the loss of the longer moment of the mono-vision setup.

 

Photoline on mount Resize.jpg

 

I use a mirror diagonal (Baader) because my experience with this scope and the prism was that the prism caused noticeable fringing. 

 

As for the mechanics, most scopes come with larger focusers today and for a binoviewer ready scope, I would make sure that the focuser is at least 2.5 inches, but this has kind of become the base focuser size these days. The reason this is important is because if you take 90mm out of the tube length, you move the front of the focuser closer to the light cone, and if you get too close, you can shave the outside circumference of the light cone off a bit, which reduces aperture. This is one of the reasons that it is hard to convert fast achromats too good binoviewer platforms. When you cut a lot off of the tube, because the light cone for something like a 102mm f/5 is pretty steep, and cutting off three or four inches of tube usually puts the front end of the focuser tube into the perimeter of the cone. If you ever want to modify a scope, I recommend doing carful measurements. 

 

The obvious advantage of the binoviewer ready instrument is that it allows you to reach focus without having to use an expensive T2 diagonal and GPC. When the extension is 90mm or 100mm, when you remove it, you can use your 2" diagonal and still reach focus with no GPC.  As mentioned earlier though, if you are using a color free Apo, when you use it at high power on bright stars, planets, or the moon, unless you use a GPC, you may see color fringing and suffer a tiny tiny loss of contrast. In most cases though, the binoviewer ready scope will reach focus both without a GPC and with a GPC, especially the 1.25x GPC and in my case (and probably most cases of binoviewer ready scopes) I can also reach focus with the 1.7x GPC. The fact that you don't have to use an expensive 1.25" mirror diagonal  (if you care about color) and a bunch of adapters means that this will often offset the price difference between a BV ready and a non BV ready instrument

 

Speaking of GPCs, I use the 1.7x, which we know actually gives more like 1.5x, but sometimes I wish I had the 1.25x GPC and I will get more into that later. When doing most low power observing, the color fringing is virtually impossible to see and except for double stars and solar system work, I do not use the GPC.  When I do solar, lunar, planets, or double stars, I use the GPC. 

 

Mostly I use this scope for double stars and larger clusters. For lowest power work, I use an inexpensive pair of Celestron XL 25mm eyepeices with a 60 degree apparent field and a field stop of 26mm.  I know I could get a bit wider field with some 24mm pans or ES 24s, but the improvement is slight. The 24 Pans are stupidly expensive and the 24mm ES eyepieces have a rather fat top and short eye relief. I don't mind the smaller apparent field given that the true field is almost the same.

 

As I said though, most of my use of this scope is doubles and planets. For doubles, I tend to use the GPC and the Baader zooms because this allows me to get a bit bigger field at low power to locate the target and then zoom in for the split. The GPC is there because for me, a great part of the joy of doubles is when they are color contrast doubles, and here, even a slight amount of color fringing can make you think you are looking at a blue star rather than a white or yellow star.  This is why the FPL-53 was important to me as well. When I view doubles, I want to see as close as possible to the actual color of the stars and not have any blue fringe influence the color I see. The Baader zooms, when used with the GPC, give about 170x, and while I can get more power using my 3-8mm zooms, this is about the most I usually need for doubles.   

 

Last night, I viewed about 15 doubles. Most notably, Sirius, which was low in the sky on a night of so-so seeing, but even under these conditions, it was an easy split, with the Pup well separated from the primary. I had a couple of 6" scopes sold as "Apos" that did not provide a view this good due to the less than color free optics. Here, Sirius and the pup looked white, with no veiling glare.

 

Keid (Omicron2 Eridani) is a great example of a case where the mirror diagonal an the GPC would be important.  Keid has a yellow-orange primary. It is nothing close to being a hard split because the secondary is well over 1 arc minute away, but the beauty here is the color of Keid and it's very faint but distant companion. I was easily able to see the yellow-orange color though, and that gives me pleasure. 

 

32 Eridani is also a yellow-orange pair, but it is not at all a tight split, so once again, the goal for me is to get the real color.  

 

 

Eta Orionis is a blue-white star. Without a GPC, you would see the star as more of having a blue fringe than being a blow white star, but with the mirror, the very small disk of the star itself was clearly blue-white and the 1.8 arc second separation is tight, but the spit was clean even using the Hyperion zooms. Here, I did put in my 3mm to 8mm zooms, and 6mm (227x) provided the best view. Both stars seemed blue white to me, but the companion is a full mag and a half dimmer so much harder to see. 

 

I did about 15 doubles though, and with the GPC, I mostly used just the Hyperion zooms.

 

This was my first time to see the Double Cluster in this scope (which I have only had for about 10 months). For this, I took out the GPC and used the 25mm E-Xcel eyepieces. The view was perfect. Even though I live under bright skies, the field was still reasonably rich with stars and the fidelity of of the view was amazing. While the clusters were the big show, the field was well populated with Milky Way field stars.  I spent some time just sweeping around this area as I find it to be a very pleasing area with differences in star density easily seen in the 1.6 degree true field.

 

On a side note, I did put in my image intensified eyepiece, and not of interest to most, I was even able to use it with my .73x focal reducer. The reducer is primarily to correct coma in very fast reflectors, but the binoviewer ready scope allows me to use it because it needs a lot of inward focuser travel. My intent is to get a .5x reducer and I am confident that I will be able to reach focus with it. With the Image Intensifier, though, it was more like looking through a 12" to 14" scope. The clusters themselves revealed many more stars and the surrounding sky was dense with stars.  The field stop is only 18mm, though, but with the reducer, this still gave me a field that was quite large. 

 

Saturn was tiny and low, and seeing was not great, so I did not spend more than a moment on it.

 

Jupiter was high, but again seeing was not great, but still, I had a view that I was better than the 10" sitting right next to it. Larger scopes are much more affected by seeing than the Apo is, and this is one of the reasons I like the Apo for planets. Most nights, I can get a very good view, and last night was not as good as typical, but still a very rewarding view.  For this I used the 6mm setting and GPC, so power was about 227x, but I did briefly 273x, a power that I can use well in good seeing but here, the 6mm setting worked best. There was little low contrast detail visible, but the belts and bands were obvious, though in a small aperture like this, you don't get the deep color you would get using something like a 12" reflector, which was my best planetary scope ever.  Still, it was a beautiful sight and enough detail to make it worth seeing. I spent about 10 minutes there. Earlier I mentioned the 1.25x GPC, and using that GPC would let me better utilize the 3mm to 8mm zooms. With the 1.7x, the higher settings really are not useful, but the 1.25x would give me lower powers and more useful powers with both pair of zooms and with the 25mm eyepieces, which means I would probably get away without having to take out the GPC for most viewing, but always have 0x as an option for rich field viewing (or as rich as it gets using a 1.25" eyepiece pair).

I did use the intensifier a bit in the Apo with the .73x reducer on some nebula. Orion was spectacular, as always, looking like a black and white picture, of this vast and spectacular showcase object. The Flame nebula though was visible, but not very bright. This is nothing to do with the aperture. Image intensifiers like a fast focal ratio, but now that I know I can reach focus using a reducer, at some point I will pick up a .5x so I can use the Apo at f/3.5, which should be pretty awesome.

 

Anyway, if you love using two eyes to view, there are a lot of advantages to using a binoviewer ready refractor. The physical shortening of the system is actually a very big plus in my book. I was able to view everything I saw last night sitting in my observer's chair, though I had to use almost the entire range of seat heights. If I were using a non-binoviewer ready telescope, I would not have had the comfort unless I chose to use a larger tripod or taller pier, which gives up some stability and may mean having to stand to view low in the sky.

 

If you are ever in the market for a refactor and you like binoviewers, I highly recommend that you find a binoviewer ready refractor. Sadly, few are sold in the US. The Stellarvue 127D is a notable example of a scope that is binoviewer ready and it was a scope I almost bought, but there were a few reasons I decided to go with the Photoline and in the end, I think it was the right decision for me.  Telescope Service offers a variety of binoviewer ready refractors but for some reason, the US importers and dealers don't seem to carry much so you may have to import if you want BV ready. It seems that several European vendors sell BV ready instruments. 

 

The new year has been with us for only 11 days, but I hope yours has been starting off great!

 

Have fun out there!

 

 


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#2 Spikey131

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Posted 14 January 2024 - 11:09 PM

I have a setup similar to yours, but I use the Baader Maxbright 2 with the Zeiss T2 Prism.  I use pairs of Panoptic 24 and 19mm, and a pair of Baader Zooms.  With the AP130GT, I am able to reach focus with no GPC or any of the Baader GPCs.  Despite the prism diagonal, I have never noticed any false color, but I always use a 2.6x GPC for high magnification.

 

I virtually always use the binoviewers for solar system observing, but I also use them for DSOs at times.  I was just out tonight watching the Io transit, and shadow on top of the GRS.  But I couldn’t resist a tour through M42, M34, M35, M36, M37 and M38.

 

I also viewed some bright doubles.  I have found that I need to be careful here because the binoviewers produce “ghost” images which can look like secondary stars.

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#3 Bintang13

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Posted 18 January 2024 - 12:38 PM

Hi,

I usually binoview with a 1.25” Baader diagonal using a heavy duty quick changer to attach the Maxbright 11 to a TS 102 f11 scope which is binoview ready. I would like to try to use a 2” diagonal as suggested here. My problem is adding a Baader gpc to this setup. How do you guys get the gpc to sit in the 2” nosepiece without movement mine moves a little regardless of which spacer I use. Is there another way to attach the gpc to this setup that I am missing.

 

I really want to thank everyone for sharing their knowledge experiences problems and solutions. This forum has been invaluable.

 

Jim



#4 Eddgie

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Posted 18 January 2024 - 04:01 PM

Hi,

I usually binoview with a 1.25” Baader diagonal using a heavy duty quick changer to attach the Maxbright 11 to a TS 102 f11 scope which is binoview ready. I would like to try to use a 2” diagonal as suggested here. My problem is adding a Baader gpc to this setup. How do you guys get the gpc to sit in the 2” nosepiece without movement mine moves a little regardless of which spacer I use. Is there another way to attach the gpc to this setup that I am missing.

 

I really want to thank everyone for sharing their knowledge experiences problems and solutions. This forum has been invaluable.

 

Jim

I use the dovetail on the binoviewer because I use the binoviewer on multiple scopes.  The dovetail has the threads for the GPC inside. Be aware that if you use it in the dovetail, you will have to remove the lens retaining ring on the GPC and flip the lenses (they are cemented, so no worries about messing anything up). 

 

I have thought many times about putting the GPC into a filter wheel, so I could just roll it in and out of the light path as needed. 

 

Anyway, to if you are using the dovetail, you just flip the elements in the GPC and screw the GPC into the dovetail. 

 

gpc.jpg


Edited by Eddgie, 18 January 2024 - 04:07 PM.

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#5 Bintang13

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Posted 18 January 2024 - 04:17 PM

Thank you so much Eddgie the picture really helped.

 

Jim




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