25 May 2012

Spring Cleaning Part 2

Eyepiece Cleaning Supplies
How often do you clean your eyepieces? I haven't cleaned all of mine in ages. I typically clean one that is in obvious need, but rarely do I attack all of them. The greatest need seems to arise after public observing events where 'junior' puts his finger squarely on the eye lens and asks 'is this where I look?' Unlike my male counterparts, I also have the mascara issue. I have a feeling that mascara is really bad on lens coatings so I try to avoid mixing the two, but that doesn't work with the public.

This spring I decided to clean all of my eyepieces - I have a modest collection of early TeleVue Naglers and Widefield eyepieces. For years I've used an air bulb to remove debris, and Kodak lens cleaning solution to get the greasy kidstuff. I haven't been happy with that result, so I consulted my mirror-making friend Jim. He has a real eyepiece collection. His requires a kid's wagon for transporting some 80 eyepieces in the collection. With that many eyepieces, one gains some experience in cleaning.

Jim recommended that I get a new box of cotton swabs (Q-tips), a new can of compressed air, ROR lens cleaner and a new can of acetone. ROR is short for Residual Oil Remover, and I found it in my local camera shop. ROR is also online at http://www.ror.net . Once I gathered my supplies and eyepieces, I headed over to Jim's for some on-the-job-training.

Jim's method is this:
1) Use compressed air (held vertically and not shaken) to blow off debris. I like an air bulb as it doesn't go empty.
2) Use a drop or two of ROR on a swab to clean the lens. Swab all glass surfaces gently. Use the back end of the swab to dry off the ROR. Repeat until the lens surface looks clean, or the ROR is no longer removing gunk.
3) Use a drop or two of acetone on a swab to clean the surface. The acetone dries very quickly so drying with the back side of the swab is probably not needed.
4) Continue alternating steps 2 & 3 until the lens is clean. I mean really clean.
5) Last, a little breath on the lens followed by a very light swabbing reveals any lingering gunk or a pristine lens. In the former case, go back to step 2.

As I worked through my eyepiece collection, I built up a nice pile of dead Q-tips. Although it seems like waste, it really isn't. They are a key component in the cleaning ritual and a dirty Q-tip is a bad Q-tip. Just use 'em.

Since my eyepieces were overdue for cleaning, I repeated the process on the field lenses of each eyepiece. Now the whole collection is ready for photons - at least until the next finger pokes at an eye lens!

21 May 2012

Spring Cleaning

The southeastern US has emerged from pollen season, so it is time for the annual optics cleaning chores. I try not to clean my telescope mirrors more than once per year. They are covered when stored, but dirt finds its way on to my optics during both storage and observing.

For years I have used a cleaning formula passed down from a professional optician (thanks Don!) Generally, I use distilled water + 91% isopropyl alcohol + a drop or two of biodegradeable detergent. I use sterile cotton to gently swab the surface from the center outward, and I rinse very thoroughly with distilled water. Last winter, I washed my 14.5" mirror and I skipped the swabbing step since the coats were new, but some haze was left behind. Lesson learned - do the gentle swabbing.

After debating the use of isopropyl in mirror cleaning with my mirror-making and telescope-building friends, I decided to track down Jeff Decker, owner of Majestic Coatings, while attending NEAF last month. I wanted to get his recommendation since he coated my 14.5" mirror. I wanted a professional opinion on the isopropyl issue.

Fortunately I found Jeff and was able to discuss cleaning at length with him. We talked about the process and materials that he used on my mirror. Jeff recommended using isopropyl wipes (see below) to gently swab the surface of the mirror. He explained that since the overcoat is silicon dioxide (quartz), the isopropyl should not damage the underlying reflective coat (aluminum). I explained that I had made mirrors for years and that seemed very aggressive, but he reassured me by offering to recoat the mirror should any damage arise.

Given the discussion with Jeff, my mirror cleaning ritual has changed a little. I still use an air bulb to blow dust off the mirror first. Next, I rinse with distilled water and then soak in distilled + a tiny amount of biodegradeable detergent. I rinse after the soak with lots of distilled water, and I blow dry with the air bulb. Finally, I swab very gently with the isopropyl wipe. The wipe I used was very saturated, so I did a final rinse with distilled water and blew off all remaining droplets of water with the air bulb. My mirror is as clean as new now (and the air bulb wore out my hand muscles!)

The isopropyl swabs recommended to me by Jeff  are Clearview wipes from CleanTex. You can find them at http://cleantex.com/old/products/presaturated/clearview.htm . If my coats begin to fail over the coming year, I'll take Jeff up on his offer to recoat. Since Majestic has been in business for years, I anticipate no problems. Instead I expect to have a clean, happy mirror.

Next time - eyepiece cleaning.

03 May 2012

The Elusive Implication of Surface Brightness

I saw the following question on CloudyNights.com regarding the visibility of extended objects and surface brightness:
"What I am interested in is finding some way to calibrate surface brightness to the chances of seeing the object in my scope."

This seems to be a popular feature for planning software. I find it a fascinating topic and I have studied it myself. My general feeling is that the ideas described in Roger Clark's Visual Astronomy of the Deep Sky help to address the question, but these alone are insufficient.

I was delighted to see this response to the question above from Sky & Telescope's Tony Flanders:
"Nobody can give you a formula that will accurately predict an object's visibility -- thank heavens!"
He also explains:
"Another way of looking at it is that the aperture of your telescope places a limit on the total magnitude of the objects you can see. And the quality of your skies places a limit on the surface brightness of the objects you can see."
I like Flanders' analogy. Clark's ideas describe the importance of the difference in contrast between the sky and the extended object. My own study has also identified several additional metrics: sky conditions, weather, personal visual acuity and sensitivity. It is indeed hard to fit all of these elements into a mathematical model that accurately predicts whether an object can be observed.

A visibility prediction feature will find its way into Deep-Sky Planner, though I am still studying the problem now. When it is released, I will state plainly that the prediction is only a model that invites further improvement over time. I truly doubt that a completely accurate model will ever be devised, so an adaptable model is probably the best we can do. That is the current requirement in the Deep-Sky Planner development plan.