Tips to Improve Telescope Performance

Comments after 50 years of observing and telescope making, by Mel Bartels

My list is quite different from the usual run of the mill lists because I have found that improving myself, not obsessing over the telescope, the key to deeply satisfying sessions at the eyepiece.

I have found three factors, in order of importance:
  1. The observer
  2. The skies
  3. The telescope

I've seen too many cases where an experienced observer sees more from urban skies than a beginner from dark skies.
I've seen too many cases where the telescope is blamed when the problem lay with the observer or the skies.

Let’s dispense with the myth that aperture makes all the difference. One of the greatest observers of all time, Stephen O’Meara, uses a 5 inch [13cm] telescope. I’ve seen expert observers work their magic with telescopes regardless of the telescope’s aperture and quality. I’ve never seen an increase of aperture turn a so-so observer into a great observer. I have witnessed amateurs regrettably leave the hobby after quickly jumping up in aperture or purchasing expensive high-end telescopes, their dreams unfulfilled. A common progression goes like this: entry level middle of the road scope, then a larger aperture scope followed ultimately by the realization that aperture does not make the observer followed by stirring a smaller scope into the mix. Advanced amateurs favor telescopes optimized for their favorite objects: giant telescopes for clusters of galaxies, long focal ratio scopes for lunar and planetary, very portable scopes for traveling to dark skies.

To an experienced observer, transparency is everything. A wonderfully transparent night renders aperture insignificant. Every telescope becomes a winner on an exceptional night. Use weather forecasts along with Clear Sky Clock to target those transparent nights. Learn to look for signs of excellent transparency during the daytime such as blue sky right up to the edge of the Sun (mask the Sun with your hand), jet trails (the trails should be short, not stretching across the sky, indicating a dry upper atmosphere), and clear sunsets and sunrises.

Here are my top tips.
  1. Remove the lens cap. Seriously. It's happened to the best of us, leaving a stop-down off-axis mask in place all night, wondering why the views are dim, wondering why that object cannot be found.

  2. Overcome your cognitive biases. Most amateur beliefs about telescopes and observing result from bias, are simply not true, and seriously limit your observational results.

  3. Observe, observe, observe. There is no substitute for hours at the eyepiece. How often do you observe a week? What can you do to increase your observing hours? Make the telescope more portable, join others observing. Aim to observe one to two times a week on average.  Malcolm Gladwell’s book, “Outliers”, states that thousands of hours of practice are necessary to become an expert. How many hours do you think that Stephen O’Meara has observed? How many have you?

  4. Keep an observing notebook.  Sketch, sketch, sketch. It’s not about the drawing as much as it is about your skills to notice detail. Study the objects ahead of time. Locate them on a planetarium sky chart and note how best to star hop to them.

  5. Dark adapt your eyes and work to keep them dark adapted. Use an eyepiece shroud. A variable brightness dim light flashlight makes a big difference. And set your planetarium programs on tablets to night mode along with red or green covers that further dim the light.

  6. Learn how to use your eyepieces. Ever watch attendees at public star parties use your scope for the first time? They move their eye around searching for the field, in and out, left and right, up and down. You too need to learn how to position your eye and how to observe the field of view for each eyepiece. If you must use glasses then be sure to pick eyepieces with sufficient eye relief.

  7. Take time at the eyepiece for each object. More time spent observing an object is like increasing the aperture and resolution of your telescope!
    A few minutes brings awareness to detail that’s thrilling and satisfying but do not stop there. More awareness and detail comes after observing for an hour or more on an object. The most difficult objects are only there 20% to 50% of the time. The seeing will stabilize and your concentration will be at your peak with your eyes paying attention to the proper place in the field for a few moments. My personal standard is that I have to see the object or detail in question three times over a 20 minute session to say that I ‘saw it’. Observe for yourself. The vast majority of observers are truthful to themselves, knowing or not caring that they will fail to convince doubters. It’s all subjective. Look at sketches by observers. Each observer tends to notice or emphasize certain features. They can invariably be traced back to digital images, to reality. I study digital images ahead of time, to get a sense of detail that might be glimpsed. If I see it, great; if I don’t, that’s great too. Knowing that it is beyond my observational powers is worthwhile too. I certainly add the negative results to my lists of “impossibles” to go after on those rare nights of perfect transparency when I find myself under the darkest skies.

  8. Get a dark sky or nebula filter. These filters really help to make subtle detail more noticeable. A filter is more important than aperture because a nebula filter increases contrast more so than aperture.

  9. What can you do to increase comfort at the eyepiece? A better observing chair, rotating the focuser to a better viewing angle, a small table next to you for your eyepiece case, tool chest and tablet, eyepiece cases that make it easy to retrieve and swap eyepieces. Use a checklist for your gear. I have a couple of checklists, one for short trips and one for longer multi-night star parties.

  10. Try different eyepieces, try different filters. Walk away for a minute then return to the eyepiece. Aim the scope at different points in the field of view. Test your exit pupil by using your lowest power eyepieces. Calculate the exit pupil of the telescope-eyepiece by dividing the eyepiece's focal length in mm by the scope's focal ratio, e.g., a 20mm eyepiece used with a F5 telescope gives an exit pupil of 20/5 = 4mm. Defocus slightly to see if you can see the primary mirror's edge (hint: look for the edge clips). If so then your eye covers that exit pupil. Borrow lower power eyepieces from friends until you find your eye's limit. You may be surprised by how big of exit pupil you can use.

  11. Consider the interplay between aperture, magnification, apparent field of view and exit pupil. Aperture sets star brightness and magnification along with field size given a standard set of eyepieces. Magnification sets the image scale. Apparent field of view sets the overall width of the field. Some like wide fields, others like narrow fields. Eyepieces designed for wide fields perform slightly differently than narrow field eyepieces. Finally, exit pupil sets background brightness.

  12. Drink water during the night, rest your eyes periodically, don’t strain your eyes during the daytime with bright light - instead use good sunglasses, have snacks on hand to fight off tiredness and dress warmly in layers.

  13. Attend observing oriented star parties like the Oregon Star Party. Talk to the top observers (like Chuck and Judy Dethloff and Howard Banich) and read their writings. Usually in their introductory comments and occasionally while talking about their observations, they will mention what they do to improve their observations. Read their comments a second time and then a third time.

  14. Find dark skies. Enough said.

  15. Baffling is the single greatest improvement that you make to your telescope. Improve the telescope’s baffling until you cannot detect any glare through your eyepieces from a flashlight aimed at various angles at the telescope by a friend. Most important are the focuser baffle, the diagonal baffle and the primary mirror baffle. For more see my diagonal baffle calculator.

  16. Optical alignment or collimation. Keep it simple: precisely center dot your primary with a notebook ring, use a good laser collimator to adjust the secondary until the laser points exactly in the center of the primary (rotate the laser to confirm that there is no wobble or angle to the laser), finally adjusting the primary so that the return beam coincides with the start of the laser beam. For more see my page on optically aligning a F3.0 telescope.

  17. Add tracking to your telescope if the field of view is under a degree. Motorize the equatorial mount, computerize and motorize the altazimuth mount, or place your telescope on an equatorial platform.

  18. Cooling the primary mirror to the night time ambient temperature. A 0.1 degree difference within the primary mirror amounts to a tenth wave error.

  19. A precision focuser with a two stage knob, particularly if the focal ratio is very short. The zone of good focus on a F3.0 mirror is a thousandth of an inch.

  20. Advanced observers should consider a second telescope specialized for their interests.
What about the endless myopic discussions on internet forums? I offer one word of advice: pay attention to experienced telescope makers who are also experienced observers. Two joys await the amateur astronomer: making a telescope then using it to view the heavens. Each telescope made is a departure from the previous telescope as the maker applies hard won lessons to satisfy desires. Lessons learned at the eyepiece by the telescope maker are lessons of hard truth. Search out these people as they are often busy observing and building.

What about exquisite optical quality and high end equipment? It’s natural to want the best; we all strive for it, but will it magically endow you with hundreds of hours of observing time? At star parties I tend to gravitate to the humble observer with the used looking telescope, maybe a bit scuffed up from many nights of use, with optics of decent quality. For example, thanks to the Demonination Bias, amateurs will pay much more money for a 1/12 wave mirror than a 1/8 wave mirror, yet the difference between these two ratings is far smaller (three times smaller) than the difference between 1/4 wave and 1/8 wave, a difference in some cases that is worthwhile.

The beauty of the Universe, stunning and sublime at once, draws us all. May you find yourself under stars observing the next clear night! 
   

References:
--- Amateur Astronomer's Handbook by J. B. Sidgwick
--- Deep Sky Companions: Hidden Treasures by Stephen O'Meara
--- Nebulae and how to Observe Them by Steven R. Coe
--- The Night Sky Observer's Guide Volume 1, by George Robert Kepple nad Glen W. Sanner
--- Observing Handbook and Catalog of Deep-Sky Objects by Christian B. Luginbuhl and Brian A. Skill
--- Philip's Obesrver's Handbook Astronomy from Towns and Suburbs by Robin Scagell
--- Visual Astronomy of the Deep Sky by Rober N. Clark
--- Webb Society Deep-Sky Observer's Handbook, Volume 5 Cluster of Galaxies, by the Webb Society Kenneth Glyn Jones, editor
--- my web article on Visual Astronomy
--- my web article on observing dark nebulae

eod