JATObservatory

Attaching a 300mm camera lens to the LPI                                                        

Recently on one of the Yahoo groups I read a posting about a gentlemen who attached a Meade LPI to a telephoto camera lens and used it for astrophotography. After reading that post I started thinking about the camera lenses I had sitting around that I could attach my LPI to.

 

The first lens I decided to use is the Russian made MC Rubinar Macro Telephoto shown above. It was original designed to be used on Russian Zenit cameras with 24x36 mm format. The lens uses  11 elements in 7 groups, has a 300mm focal length a fixed  aperture of F4.5 and  has 77mm threads on the front. The rear of the lens has a M42 screw mount. I have other M42 mount lenses that I use on my Canon 10D digital SLR. They are attached via an M42 to EOS adapter. The problem with this particular lens is the diameter of the lens does not allow it enough clearance to mate close enough to the 10D's body to allow infinite focus. It will only focus out to about 50 ft when mounted on the 10D. (But it does perform extremely well as a macro lens on the 10D).  Because of the M42 threads, 300mm focal length and fixed aperture I decided this would be a good candidate to attach to the LPI.

Here is a picture of the M42 thread on the back of the lens. It is important to try and keep the distance between the rear element on the lens and the LPI's CCD chip as short as possible.

Two adapters where used to attach the LPI to the Rubinar lens.  The good thing was both adapters are  items that I found by digging around in my box of adapters. The adapter on the left is a standard .9 of inch "T" extender. It has a standard set of  male and female "T" threads on the ends. I screwed this adapter to the M42 threads on the back of the Rubinar lens. Even though the threads are not a match I was able to apply 6 or 7 turns before the threads get tight. Once they get tight I do not force it as I don't want to strip the threads. I know the correct method would be to find a M42 to "T" thread adapter, but I don't want to spend any money on this project, well not yet anyway.  The adapter on right is a 1/2 inch "T" thread onto 1.25" eyepiece adapter. (It was originally used to attach an eyepiece to the visual back of my ETX90EC). I screwed this to the "T" extender. The question you are now wanting to ask is "why not just screw the eyepiece adapter directly to the Rubinar lens"? The answer is you can't. Without the extender, the eyepiece adapter  makes contact with the last of the elements on the lens, and won't allow the threads to mate. The good news it even after using both adapters, the lens will still achieve infinite focus. But no there no chance of me being  able use a diagonal in this optical chain.

The finished product. A single 3.5' mounting ring was used to securely hold the lens. I wasn't sure how I was going the hount the lens, but this mounting ring workeds great.

 The LPI (silver) can be seen attached to the rear. The LPI shown in this image is covered with aluminum tape. The reason is I also use the LPI for solar imaging. What I found is the top part of the case on the LPI lets light through. This stray light causes glare when it hits the camera photo chip.  Obviously this is not an issue when using the LPI at night. But during the day for solar images it was a problem for me. The glare caused a lot more post image processing to remove the glare.

These images show the drastic difference between  the stock LPI case, and then after it was sealed from stray light. These images were taken just a few seconds apart.  No processing was done to either image, and no animals were injured  during the testing.

 To test the setup I mounted it on a tripod using the standard camera mount threads on the bottom of the mounting ring. The other thing you may have noticed about this lens is it has a center obstruction. That because is uses a center mounted mirror just like a SCT, (which is why the lens is so compact even though it has a 300mm focal length).

Here is an image of some flowers in my neighbor's yard. They are about 250' feet away. This a single LPI non stacked image.

I decided I wanted to try a quick image of the Sun so I took the dew shield off of my Short Tube 80 and my modified ETX90 white light solar filter and.......

...attached them to the Rubinar lens! The focusing had to  be done before the solar filter is attached. The plan for the future is to put some high density foam between the dew shied and the focusing ring. This way I can just spin the dew shield to focus.  I just pointed the camera at the Sun while it was on the tripod and made a AVI using the ToUcam software.

This is a single frame image extracted from the sun AVI  that was created. It  has been heavily compressed so it is "web" friendly, but is still about 4 meg and lasts about 50 seconds. As you can see I didn't spend a lot of time focusing on the Sun or playing with the color balance. Somebody must have cleaned the Sun today anyway because there wasn't one sunspot anywhere on it's face all day.  If you want to view the video  click here.

These 2 photos show the LPI and the Rubinar mounted "piggy-bottomed" under my 10" LX200GPS.

Attaching a 50mm camera lens to the LPI


Another yahoo post requested info about attaching a 50mm lens to the LPI. So I decided to try. Again I dug through my bag of adapters and returned with  the ETX90 visual back adapter along with an adapter I purchased from SBIG. The lens I decided to attach was a 50mm lens from my old Ricoh XR-10M film camera.  The reason I choose this lens is because I knew I already had the Ricoh (Pentex) SBIG lens adapter. This adapter was originally purchased in order to attach the Ricoh lens to the Meade 416 CCD camera. 



Here you can see the unassembled chain of parts, with the LPI on the right and the 50mm Ricoh lens on the left.


The adapter that attaches to the lens is configured the same as the camera body the lens would normally attach to. It has the red dot so you know how the orientate the lens . This adapter was purchased from SBIG. They make adapters to fit most of the common camera lenses (just remember these adapters were designed to work on their cameras). The assembled lens and the first adapter is shown. Notice the T-threads on the right side. These will be used to attach the eyepiece adapter.


The next step in the chain is the connection between the lens adapter and the eyepiece adapter that will attach to the LPI. For this Meade's 2-piece visual back to eyepiece adapter for the ETX90 was used. In order to use this adapter it has to be separated, by unscrewing the 2 pieces. Only the part that contains the thumbscrews and the female T-threads will be used.


Once the ETX90 adapter is separated it can be attached to the SBIG adapter's T-threads.  The LPI will connect to the eyepiece adapter using the 2 thumbscrews. .


Here are 2 images of the completed adapter with the LPI attached. As always remember the distance between the lens and the camera's chip is important. If the distance is to great you will not be able to reach focus. The only problem with the above setup is there is currently no mounting point to attach the assembly to a tripod or piggy-back on a telescope, so I just used tie-wraps to attach it to a tripod in order to take the photo below.


This picture was taken inside looking out through a sliding glass door, using the Ricoh 50mm lens and the LPI. The grey house is about 250 yards away. The beige shed is about 125 yards. The basketball net is about 75 yard. The pool is about 50 yards and the fence is about 15. The setting on the LPI were as follows: Gain = 100 , Offset = 50, Exposure = .063. The terrestrial setting in the LPI software was used. The F-stop on the Ricoh lens was set to F/16. It is a overcast day.

Attaching a 180mm Fisheye camera lens to the DSI

Another on going project I have is to build an All-Sky camera similar to the one on the Night Sky Live website. I decided I didn't want to dedicate my Starlight Express MX-7C or Meade 416-XT camera for this task and the LPI is not sensitive enough. Then my hope was restored when my Deep Sky Imager arrived.  Earlier on I talked to the folks that run Night Sky Live about those rather cool CON-Cam cameras because I was interested in acquiring one. I was told that no more where available until next year, but the price would still be the same, around $20,000! That was a bit more than I was willing to spend. So I decided I would consider building my own at, but I only wanted to spend a faction of what the CON-cams cost. 

 I have managed to mount a 180 degree fish lens onto the DSI. The current problem is because of the size of the DSI's CCD chip I get a FOV that is more like 140 degrees instead of 180 degrees. My next plan is to try and attach a focal reducer internally to the setup. I am hoping this may allow me to get the whole 180 degree FOV back. The camera will be mounted in a bell-jar type cover to keep it dry and has  a muffin fan attached to the heat-sink to keep the camera cool as well as ventilate the enclosure to prevent condensation from forming inside.

For the lens a 180 degree 8mm F3.5 fisheye made by Peleng was used. The 1.25" nose-piece on the DSI is removable. The problem is with other Russian lenses is the Peleng uses M42 treads which as above don't match the standard T-treads on the DSI. So the nose-piece will be left in place on the finished project, and the same type adapter system that was used to attach the 300mm lens to the LPI will also be used here.


 

This above example is just one of many. There are many different lenses, and a host of Astrophotography cameras you could use. Adapters are commercially available for many lens mounts from a number of vendors. The key thing to remember is the distance between the rear element of the lens and the camera's chip. If the distance is to large you lose the ability to achieve infinite focus. The other considerations are the weight of the lens and it's mount. Be sure you mount your lens securely, be it on a tripod or piggy-backed on a telescope. If you secure the lens and camera so it does not flex, and providing the lens has long enough focal length you can use it as autoguider.

Other CCD imagers and camera lens

I also snapped these pictures of my Starlight Express MX7C (shown on the right) and Meade 416XT CCD cameras attached to the the lens. The MX7C mated directly as it has the correct threads. For the Pictor I had to use the extender. I haven't verified  to see if I can still reach focus with the Pictor or the Starlight Express. I don't expect I wil  have any problems with the MX7C as the CCD chip is fairly close to the end of the camera's barrel, so the distance between the lens and chip are minimal. But I will have to get out and test all these configurations under the stars.

 

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Updated 11/27/2015 - Please report broken links jato@jatobservatory.org