Why I Bought a Vixen VMC110L How I Like It
My current scope is an Astro-Tech 8 in. Imaging Newtonian mounted on an AS-GT (CG-5) mount. With my coma corrector and Canon Rebel XT, I have taken a few nice pictures and I am very happy with my setup. My guide scope is a little 70mm Travelscope with a webcam and laptop. Thing is, the AT8in only has 800mm focal length. This leaves smaller objects like planets and planetary nebulae looking tiny, and I just cannot get the resolution I want on the small objects.
I tried using a Barlow with the AT8in, but it screwed up my coma correction. I only have a Celestron Ultima 1-1/4 Barlow, so I cannot put it in FRONT of the coma corrector, which would preserve the distance between corrector and camera sensor. I have to use it in the eyepiece adapter and that ruins the correction.
I also tried the 1-1/4 Barlow direct to the camera without the coma corrector, but I still get bad coma at the edge of the field. So why not just buy a 2 in. Barlow, you say? Well, for quality glass that will not cause distortions, the price is on up there. In fact, the $140 I paid for this new little scope would not get me a good 2 in. Barlow.
So, here is my logical solution. I can use the big daddy AT8in for all my deep sky stuff. It can pull in the galaxies with that huge aperture. I can use the VMC110L mounted on top with my webcam as a nice guide scope. When it comes to smaller targets, I can just reverse the cameras. I put the webcam in the 8in as a guide and put the Canon XT on the straight-thru port of the VMC110! (overkill? I think not!)
I also intend to take the VMC110L on business trips as my true travel scope. It fits nicely in a roll-aboard suitcase along with a medium duty SILK tripod. With that, my webcam, and laptop, I can get quality shots of the moon and planets from some nice dark skies.
So, how do I like the scope in actual use? I think it is fantastic!
The construction is very sturdy. You get metal, not plastic where it matters. The tube, dovetail, and eyepiece holders are all well made. The eyepiece holders also have threaded set-rings to allow you to adjust the focal distances to your eyepieces. This helps get a camera and eyepiece at par focal distances using the flip-mirror.
The optics are very good and well corrected. VMC stands for Vixen Maksutov-Cassegrain. It has spherical primary and secondary mirrors and a corrector lens mounted after the secondary. The difference from traditional Maksutovs is the placement of the corrector lens, which permits air flow into the tube. This equalizes temperature better than a full-aperture meniscus lens. It also reduces weight.
The views are pinpoint sharp to the edge. I was happy to regain the use of some favorite 1-1/4 inch eyepieces, and the stars stayed crisp across the field of view.
The VMC110L 1035mm focal length plus a Canon digital camera with a 22.2x14.8mm APC-S sensor will give a FOV of 73x49 arcmin. The resolution is 1.13 arc seconds/pixel. With a Philips webcam with a 7x5mm sensor, the FOV is 23x16 arcmin with 1.04 arc seconds/pixel. That resolution is probably at the limit of the seeing from most locations, and the Vixen datasheet says the resolving power is 1.05 arc seconds so it is a nice match . Someone please correct my math if those numbers are incorrect.
You can use a quality 1-1/4 Barlow with this scope to obtain +2000mm focal length. That will draw in nice small targets like Mars and still give a good bright view. Since you have a little more effective surface area than your 80mm ED refractor, you can utilize the Barlow or any filter and still have a bright view of any planet. The 110mm aperture gives a visual limiting magnitude of 12.0. That is pretty good for a scope that is about as big as a football.
It has an internal flip-mirror is a decent unit that has 96% reflectivity. I had to really dig through some literature to determine the mirror. That stat is not in the data sheet, but I believe it to be the same as a flat in another couple of Vixen products. I am sure someone will correct me if I am wrong. However, if you intend to use this scope visually, I am sure you will want a better diagonal mirror for other reasons seen below.
NOT DIFFRACTION SPIKES
I read some reviews where a VMC110L owner bemoans Diffraction Spikes caused by Too Thick Spider Vanes. I am not so sure about that one. Based on what I have seen, the straight thru port and eyepiece or camera show no diffraction spikes.
I think what that user has encountered is actually caused by the flip mirror, and associated misalignment which causes coma. The coma even in the center with the flip mirror made bright stars look like tiny + signs. Maybe this looked like diffraction to that user.
The problem with the built in mirror is that you cannot collimate both light paths. If you collimate based on the straight through port, that collimation will NOT be the same for the flip mirror. In fact, it is quite a bit off. I tried to find a way to tweak the flip mirror alignment, but no luck so far.
You should use the flip mirror and an eye-piece to center a target, and then switch back to straight thru for focusing and making the exposures. For that purpose the flip mirror is perfectly acceptable.
If you want to use the VMC110L visually, I suggest getting a nice diagonal that will screw on with the SCT threads on back. That will ensure that once you collimate it, you will not have to touch it again.
WARNING: HIGH MAGNIFICATION
The long focal length of 1035mm does come with a disadvantage. Even with a 25mm eyepiece, stars whizz by! I used a SILK tripod for my initial evaluations. The flip mirror does make it easier to center objects without a big pain in the neck. The trouble is keeping them there.
By the time you flip back the mirror and focus the camera, the object has already moved significantly. You almost have to lead it with the eyepiece view, and then work quickly to take the exposure.
Of course this is not a problem if you have an equatorial mount, but with an alt-az such high magnification comes with a price.
I think the VMC110L will serve me well as a focal length boost to my AT8in. You really do not need lots of aperture for bright objects like the planets and moon when you are using a webcam. Plus it makes a nice travel scope. At just over one foot long, and 4 lbs., it is a snap to pack with your business khakis.
I believe the optical quality, sturdy construction, and easy setup of this VMC110L will serve me well at home and on the road.
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