The Problem

Shooting from Bortle 8 skies with an f/5 scope means exposures get blown out or go white fairly quickly. Shooting long exposures is doable but with my skies and setup I’d greatly benefit by using a light pollution filter. But what type of filter would work best for my rig a 2″ round or clip-in, etc.  What’s available for my older Nikon D5100 DSLR and where would the optimum location for a filter reside in my light train?

With these questions in mind I ventured to find out. My first stop? A quick scan of the owner’s manual for my Meade Series 6000 70mm Quad APO Astrograph but surprisingly this revealed no information at all. There is this in the owner’s manual:

Not much help really and the “picture” mentioned above is not actually on the whopping 2 page owner’s manual. So after searching online for information on adding a filter to my specific scope and even calling Meade Customer Service for assistance; I got nowhere. I felt sure that a filter could be added I was just seeking assistance with the best approach.

The Test

I didn’t have a 2″ filter so I bought an inexpensive 2″ Solomark Moon & Sky Glow filter for $20 bucks off Amazon mainly as something to test with before taking the plunge and buying a high dollar LPS imaging filter. I’m glad I decided on that route. I very quickly found out that the 2″ filter did fit nicely between the 48mm to 42mm adapter that is used to connect the DSLR to the telescope. The line up goes like this:  DSLR, Nikon T-Ring adapter, 48mm to 42mm adapter, Moon & Sky Glow Filter, telescope.  Success!  Not quite. Adding the filter at this point in the light train increased the distance that the camera was from the back of the scope. By pushing the DSLR back slightly I was then unable to achieve focus. The focal point with this telescope is very close to the end of the scope with the focuser almost fully racked in. There is hardly any travel to work with. Back to the drawing board.

The Search

Since the 2″ round filter didn’t work for me I decided to focus my attention on clip-in type filters (those that fit within the camera body). This type of filter would not add or increase the light train distance any substantial way and thus would hopefully solve my problem.

These filters are not nearly as prevalent for Nikon crop sensor DSLRs as for Canon EOS models. Knowing this I still set out to find one since my 2″ filter test bombed. Being an older camera, the D5100 further reduced my chances of finding a viable clip-in but as luck would have it I found that Astro Hutech made several clip-in type filters specifically for the D5100. Hooray!  Not so fast there astro boy.

I reached out to Hutech about their IDAS LPS filters but was informed that they had stopped making the filters for the D5100 but, I was told, there might still be some supply left from a telescope supplier in Germany.

As you can imagine I was getting frustrated at this point. The price for the clip-in filter listed on the German seller’s site was expensive even after converting from Euros to U.S. Dollars, and I really didn’t want have to purchase from across the pond from a source that didn’t speak my native language. So I then tried to locate one in the Western Hemisphere.

Success! I found one in Canada. Nope. Sorry, we don’t carry that one any longer and by the way, we’ve now updated our web site to remove that item. Then another hit from an outlet in the Seattle area only to again have my hopes dashed with the same exact answer. We no longer carry that filter and have updated our web site accordingly. Doesn’t anybody do inventory on their web sites any more!?

The Solution

The search continued for a clip-in filter and, yet again, I thought I had found one at Ontario Telescope but the filter in question didn’t specifically mention that it would fit in/on the D5100 but it would fit the 5300, 5500 and 5600 DSLRs. Okay, close enough for me. I called and explained my situation to the agent and what telescope I was wanting to use with it. “Hey, wait a minute!” He says, “I own that telescope. You can take the back off that scope and thread a 2″ filter inside the telescope!” Face palm! You’ve got to be kidding me. Great, I say, and we discussed the operation in detail for a couple of minutes. I thanked him, hopped off the phone and went and pulled out the hard case containing my telescope. I then proceeded to remove the back. Sure enough, just as he said, the back was removed within moments and I confirmed that a 2″ filter would fit inside the rear of the scope.

Ironically, early on I actually attempted this very thing but failed because I didn’t fully remove the thumb screw. Backing it out most of the way is not sufficient. The three flat head screws and the thumb screw all have lubricated plastic inserts on the business ends that are pressure sensitive so they can be loosened in order for the whole housing to be rotated with the camera attached. This is especially helpful in framing your subject.

All of that and the solution was right in front of me the whole time. What a waste of time and energy. What a knucklehead I was but even more aggravating was the fact that I could not find this info clearly outlined in the scope’s owner’s manual or online anywhere. Maybe I just didn’t look hard enough? Here’s hoping this lesson and the following information below is helpful to someone out there.

Filter Installation

To add a 2″ filter to the Meade Series 6000 70mm Quad APO remove the three brass flat head screws and the silver thumb screw pictured below from the section just behind the beveled edge fitting on the back the scope.

Once all three brass flat head screws and the thumb screw have been removed gently pull the fitting off the back of the scope. See below.

The 2″ filter can then be threaded onto the inner part of the housing you just removed. Be very careful not to touch the filter while threading it on and reinserting it back into the telescope. Replace the three screws and the thumb screw and you are ready to add your camera.

As mentioned above I hope this information is helpful to someone.  The filter you see being installed in the pictures above is the Optolong L-Pro light pollution filter. I hope to have some nice images using this new filter posted very soon.

The 70mm APO Astrograph can accept 2″ filters you’ll just need to remove the rotatable camera connector on the rear of the telescope in order to thread it on the inside the housing. Additionally, you can add a filter in the light train (between adapters and the DSLR) externally but beware this will increase the distance between the camera and your back focus point. You might not be able to achieve focus with this particular method.

Clear skies!

Scott