Solar system evening

I pulled out my 8" Coulter, and spent a long time looking at Jupiter, trying different Rosco gel filters.  I think I had my most detailed views of Jupiter ever--it really looked good.  I found the emerald-green and sky blue filters the most helpful.  I then spent about half an hour trying to find Comet 103P/Hartley 2.  It was tough, because in my backyard there are only small patches of sky showing, and in that direction is a lit up street, so I had a hard time identifying a star that I could star-hop from.  Finally, I went for Zeta Cephei, which was 15 degrees away.  I then went field of view by field of view, matching the view through the eyepiece with the chart in AstroInfo.  I found the stars where the comet was supposed to be.  And then I experimented with different eyepieces.  I kept on getting glimpses of something in the area with averted vision.  And once or twice with an O-III filter, also with averted vision.  I was using magnifications between 65 and 150X.  So I guess I saw it.

I rounded out the evening with a look at the moon, another quick look at Jupiter (not as good as earlier) and then a look at Uranus.

Eyepiece case

I've found it a nuisance to take eyepieces in and out of bolt cases.  Moreover, the amount of time it takes to pack up everything at the end of an observing session limits the length of the session.  So I decided to make one of those eyepiece cases where the eyepieces sit naked and can be used right out of the box.  I initially planned to make a plywood box, but decided that would be too heavy.  Instead, I picked up a Harbor Freight steel and plastic toolcase (like this one, but maybe slightly smaller) for a low price, and made a plywood insert.  Unfortunately, the case was stinky.  The plastics in it were off-gassing.  It took about seven weeks of ventilation until it became usable (obviously, I don't want off-gassing onto optics).  Finally, today, I put the insert in--gluing it in place with silicone glue and putting some screws in.

It includes space for 1.25" and 2" eyepieces (the laser collimator occupies one of the 1.25" slots).  In the middle there is room for filters.  I drilled two holes through all my slide-mounted Rosco gel filters, and put machine screws pointing upwards on the insert for the filters to sit on.  The fit is good.  My ND and OIII filters are in a plastic box attached with Velcro (or maybe a generic hook and loop fastener) to the insert.  Finally, on the right side, there is room for my battery box (for driving fans or giving extra power to PDA), geen laser, flashlights and spare batteries.  I am quite pleased.  But since the silicone is still off-gassing, I took everything out after taking the photo.

Using three cent Rosco gel filters for planetary observing

As an experiment, I bought the Roscolux Swatchbook from B&H Photo for $2 plus $5 shipping. One can also get them free from a Rosco dealer if one lives near one (Lee also has a version). Anyway, what you get is about 250 gel filters, each 1.75" x 2.75" (with a hole that mounts it in the book) and each with a light-transmission curve. Anyway, one can then hold a filter between eyepiece and eye for planetary observing, assuming sufficient eye-relief (a reason to use long ER eyepieces). The filters are meant for stage lighting, and the small format are sometimes used for coloring a camera flash or strobe. I didn't know if they had the optical quality for actually looking through them, but thought it was worth trying, and so I ordered the set.

I had a bad experience in the past with a basic Celestron color filter set. While they occasionally may have teased something out, they scattered the light too much.

Here are my initial observations of the Rosco filters. The standard Roscolux gel filters look optically good to the naked eye--no obvious irregularities. (There are also included some special filters that are intended to scatter light. Obviously, these are unusable for astronomy purposes.) When I looked through them indoors naked-eye, I saw some light scatter around light bulbs (a small halo), which worried me a bit. (I hadn't done this test with the Celestrons.) But otherwise the image was very sharp.

I then took the set outside with my 8" F/4.5 Coulter, with a 6mm TMB/BO for 150X (I actually should have used a higher magnification, but I was in a bit of a hurry). Targets: Saturn and Mars.

I initially couldn't see any detail on Saturn without a filter. Occasionally, I got an intermittent hint of a band in the north.

I started with red filters. I could barely see Saturn through #27 Medium Red (4% light transmission). #26 Light Red (12%) was better, and occasionally--the seeing must have been quite intermittent--I got hints of a sharply defined Northern band. What worked best, however, was #23 Orange (32%). The band only appeared from time to time, but when it appeared it had a sharply focused appearance. Moreover, the filters removed the annoying CA that my TMB eyepiece contributes. I tried Moss Green (45%) but it did nothing for me.

I then moved on to Mars. Orange helped control the bloom that I get from the 1/8" thick double-vane Coulter spider, and it highlighted a dark feature near the south pole.  The ice cap was visible, too.  I eventually was able to see the feature and the ice cap without the filter, but the view was much better with the filter. Moss Green again did nothing for me.

But the really happy news was that I had none of the blurring that I had with the Celestron filter-thread filters. The rings and their shadow stayed sharp. At three cents per filter, this is a great deal.

Cons:
The filters are very flimsy--I don't know how long they'll last. Moreover, they are hard to use when in the book. I need to find some way of getting them out--simply trying to flip them out of the book doesn't do the job well. Moreover, if I hold the whole book with the filter in front of the eyepiece, the filter wobbles and the object moves, which of course makes it harder to see detail.

Pros:
Sharp images. Very large selection of filters, with a large variety of light transmissivities and for fine-tuning the choices. Includes light a transmission curve for each filter. Super cheap: get about 250 (not all astronomy-usable) for the price of one filter.

Future work:
I want to make a holder for these in my eyepiece case. I am thinking of putting up two steel rods sticking out, one for permanent storage of the filters and the other for the filters I am using during the session. There would be Velcro'ed webbing to keep the permanent storage filters from flopping away.

I also want to experiment with the gel filters as full-aperture filters. One can buy them in 20"x24" sheets for $6.50 plus shipping. In fact, one of the main reasons I got the swatchbook was so I could figure out which colors I wanted in the full-aperture dimensions. Orange is definitely going to be there.