20 to 25mm - the all-purpose focal length?

[scarp15]

That is quite a concentrated focal length area which is highly purposeful. For a while I used a 20mm T5 and (just out) 26mm T5, as said excellent eyepieces and I still recall my first (surprise) encounter with the Bubble nebula. The 21E has become my most commonly used eyepiece and works for each of my scopes between F4.6 and F7, I also use a 20mm and 25mm TV plossl. At a dark site, a 31T5 will command a good deal of used time.

[Alan White]

Oddly around 20mm is the magic mark for me with my ED80 and 150p but that is a product of the scopes as Stu suggests.
However its a magic point for me to date.

I have:

19mm TeleVue Panoptic
20mm TeleVue Plossl
22mm Vixen LVW
25mm TeleVue Plossl

At present the 25mm TV and 19mm Panoptic are in favour, but that may well change.

 

[Stu]

2 hours ago, Littleguy80 said:

Thank you, Stu. I have to admit to being surprised by that. I've not seen the Crescent nebula yet but I believe it's a relatively small target and hence thought it would be better at higher mags. Which, in retrospect, is a flawed way to think about it!

I guess it is always a balance of target surface brightness vs sky background and which exit pupil work best on a given night. This shows the scale, not as small as M57 for instance, very much larger

[Littleguy80]

2 minutes ago, Stu said:

I guess it is always a balance of target surface brightness vs sky background and which exit pupil work best on a given night. This shows the scale, not as small as M57 for instance, very much larger

Bigger than I thought. It’s one of my targets to try and see this summer  

[jetstream]

8 minutes ago, Littleguy80 said:

Bigger than I thought.

and very faint.....

[Littleguy80]

5 minutes ago, jetstream said:

and very faint.....

What eyepiece do you use for the crescent, Gerry? 

[Stu]

5 minutes ago, jetstream said:

and very faint.....

Yes, a tough one. It was interesting observing with Steve (Swampthing), he has much more experience of observing these sorts of targets and was seeing detail or structure that I wasn’t getting. A case of building up experience over the years.

[cloudsweeper]

As others say, it depends on the 'scope.  I usually start with the Hyperion Aspheric 36/72, then:

ST120 - miss that range completely and go to the ES 14/82, or perhaps the Meade 5000 UWA 20/82 for the generous FOV;

8SE - I usually go on to the ES 24/68 or  the Meade 20/82, both of which give the same FOV, but the Meade gives more mag of course.

So the answer from me would be that a 20/82 is a very useful EP - and although it's big, it's not too  big!

Doug.

 

[Littleguy80]

1 minute ago, Stu said:

Yes, a tough one. It was interesting observing with Steve (Swampthing), he has much more experience of observing these sorts of targets and was seeing detail or structure that I wasn’t getting. A case of building up experience over the years.

I’ve often wondered what makes the difference with an experienced observer. What’s visible in the eyepiece must be the same so what does the experience teach you that allows you to see more? 

[25585]

2 hours ago, Stu said:

I struggle with these types of questions sometimes because it totally depends upon the type, and most specifically the focal ratio of your scope as to whether this focal length eyepiece is useful or not.

If you take f6 as a rough average then it does lead to some comments which are comparable. In the past I have used Maks at f20, and currently have f14 which lead to a very different exit pupil and different usefulness. Trying to relate the value of a 20 ish mm eyepiece in an f20 8” Mak with an f3.7 20” dob can lead to confusion....  

That said, and in a spirit of not being (too) awkward  I do have a 24mm Panoptic which is a wonderfully sharp eyepiece giving me around 3mm exit pupil in the Tak, x30.

I also use two 25mm Zeiss converted microscope eyepieces which I use in a Mark IV Binoviewer for white light solar and also astro targets, mainly lunar where they allow me to use high powers without floaters being a problem. Ironically I rarely use them at native focal length, but normally barlow the socks off them to get down to anything around a 3.5mm effective focal length. They are very sharp, with low scatter, a nice big exit lens and good eye relief and barlow incredibly well. Amazing eyepieces.

I have owned a 21mm Ethos in the past, ‘nuff said, lovely and as John says generally giving a nicer contrast than the 31mm Nag unless under pristine skies. Also the 20mm ES 100 degree is excellent. Never had the chance to side by side them but I doubt there is too much in it. With prices as they are currently I would be ES all the way, although the Lunt has an excellent reputation and is great value, so is probably worth a try.

Fair point Stu. 20mm in my C8 gives 100x, so is not used, I stick to 30 & larger. One problem with Cassegrains is limitation of variety for lower magnification eps and especially when 1.25 fit is restricting choice. 

With a FL of 1500, 20 will give 75x, a good now-you-see-it step from finder eps such as a 35 Panoptic (in my case). 

The Ring Nebula M57 location is a good example of using both those. (Then a 13mm for just over 100x, after which alt az viewing gets tricky). 

 

[25585]

Device hiccup

[Stu]

1 minute ago, 25585 said:

Fair point Stu. 20mm in my C8 gives 100x, so is not used, I stick to 30 & larger. One problem with Cassegrains is limitation of variety for lower magnification eps and especially when 1.25 fit is restricting choice. 

With a FL of 1500, 20 will give 75x, a good now-you-see-it step from finder eps such as a 35 Panoptic (in my case). 

The Ring Nebula M57 location is a good example of using both those. (Then a 13mm for just over 100x, after which alt az viewing gets tricky). 

 

Focal ratio is one of the key factors. If, as a number of members do, you have scopes around the f5 and f6 range, the eyepieces will tend to work well across them because the exit pupils are similar. Eg an eyepiece that gives a 1mm exit pupil in one scope will be similar in the others.

As I mentioned, if you have an f20 Mak and an f3.7 Newt, you need far more eyepieces to cover all bases.

[Louis D]

10 minutes ago, Littleguy80 said:

I’ve often wondered what makes the difference with an experienced observer. What’s visible in the eyepiece must be the same so what does the experience teach you that allows you to see more? 

Patience and technique.  You learn to wait for moments of good seeing.  You learn to sweep your scope around because the visual cortex can often pick out more detail from a moving subject than a static one.  You learn to use averted vision to move dim objects to the more light sensitive rods away from the fovea.  You learn to match the magnification to the seeing conditions to maximize contrast and detail.  You learn to rack focus in and out a few times to see if detail improves from your first attempt at best focus.  You learn to move an object around a wide field eyepiece to see if it is sharper in some areas than others, often due to unseen gunk on the eye lens.  On solar system objects and a few bright nebula, you learn to prepare your cones by looking at a bright surface and then looking in the eyepiece.  You learn to still your breathing to keep your eyes more steady.  These are just a few of the things I've learned over the years to improve my observing.

[F15Rules]

My current covering of those focal lengths are:

LVW22mm - pretty much perfect to my eyes

Parks Gold Series 25mm - as above apart from a narrower for ~52degrees . Steve (Saganite), we must compare my GS 25mm and your Ultima 24mm.??.

Parks Gold 20mm - higher power version of the 25mm GS.

Honourable mentions to TAL 25mm Gen II as mentioned by Steve (Saganite)?, ES24mm 68deg (superb value for money), Meade Japan 4000 26mm plossl. (just outside)

Just outside the range, my new Morpheus 17.5mm looks extremely promising after very limited use due to the weather.

Another excellent ep close to the range is the Tak LE 18mm, wonderful as a binoviewer pair.

I'll just mention one surprisingly disappointing ep that was the Pentax XW20mm. I had really high hopes for this one, but in my refractors it was soundly beaten by the LVW22mm.. the XW had significant field curvature (it's even worse in the 14mm)..and I say that as a big fan of Pentax eyepieces - and at 10mm or shorter FL I still think they are hard to beat by any other eyepiece I've looked through ☺.

Dave

[25585]

3 minutes ago, Stu said:

Focal ratio is one of the key factors. If, as a number of members do, you have scopes around the f5 and f6 range, the eyepieces will tend to work well across them because the exit pupils are similar. Eg an eyepiece that gives a 1mm exit pupil in one scope will be similar in the others.

As I mentioned, if you have an f20 Mak and an f3.7 Newt, you need far more eyepieces to cover all bases.

Multi FR scopes beget multi FL eyepieces. And their enhancers etc. 

[Stu]

11 minutes ago, Louis D said:

Patience and technique.  You learn to wait for moments of good seeing.  You learn to sweep your scope around because the visual cortex can often pick out more detail from a moving subject than a static one.  You learn to use averted vision to move dim objects to the more light sensitive rods away from the fovea.  You learn to match the magnification to the seeing conditions to maximize contrast and detail.  You learn to rack focus in and out a few times to see if detail improves from your first attempt at best focus.  You learn to move an object around a wide field eyepiece to see if it is sharper in some areas than others, often due to unseen gunk on the eye lens.  On solar system objects and a few bright nebula, you learn to prepare your cones by looking at a bright surface and then looking in the eyepiece.  You learn to still your breathing to keep your eyes more steady.  These are just a few of the things I've learned over the years to improve my observing.

Great post Louis. Thing is, I knew most of those techniques but still Steve was seeing more. I can only think it is some form of learning process where you train your brain and eyes to see the detail over a period of time. Most of my experience has been in planetary and solar observing which needs many of the techniques you mention and using averted vision etc etc is second nature. I am confident I can pull pretty much all the detail there is to be had in a planetary, solar or lunar view. My DSO experience is however limited to a relatively few trips to dark sites on holidays, say once or twice a year, whereas Steve has been a hardcore DSO observer for a long time. There must be something in that perhaps?

[25585]

It's similar in many ways to hand held high magnification viewing, photography & sharp shooting techniques. Self-discipline and drill becoming instinctive. Always a learning curve. 

 

[jetstream]

43 minutes ago, Littleguy80 said:

What eyepiece do you use for the crescent, Gerry? 

It depends on the scope but at f4.8 I use the 20mm Lunt mostly and at times the 30ES 82. The Lunt works very well on this target. The Crescent will show really fine filamentary detail under good conditions, in my 10" and espc the 15". This object is extremely sensitive to transparency so I use it as a test of sky conditions. Under VG conditions I can see a portion of it with no filter.

[Littleguy80]

9 minutes ago, Stu said:

Great post Louis. Thing is, I knew most of those techniques but still Steve was seeing more. I can only think it is some form of learning process where you train your brain and eyes to see the detail over a period of time. Most of my experience has been in planetary and solar observing which needs many of the techniques you mention and using averted vision etc etc is second nature. I am confident I can pull pretty much all the detail there is to be had in a planetary, solar or lunar view. My DSO experience is however limited to a relatively few trips to dark sites on holidays, say once or twice a year, whereas Steve has been a hardcore DSO observer for a long time. There must be something in that perhaps?

Agree. Excellent post @Louis D! I wonder if familiarity with the targets themselves is key too. I find, even with something like the moon, comparing the view through the eyepiece to an Atlas normally results in me seeing details that I otherwise would have missed

[jetstream]

12 minutes ago, Stu said:

I can only think it is some form of learning process where you train your brain and eyes to see the detail over a period of time

I totally agree Stu and this is why I go to an object repeatedly over the course of an evening to get the object recognition going. I pick objects to go over- and- every session until they get into the memory or whatever, the Little Veil is a prime example as is the Jellyfish (and many more). Now these objects show much easier and with more detail.

[scarp15]

1 hour ago, Littleguy80 said:

What eyepiece do you use for the crescent, Gerry? 

You will know it when you see it Neil and you will get it. Quite as Gerry said, your Lunt 20mm coupled to the Astronomics OIII filter, when transparency, dark adaption, elevation are optimum. Mapstar in another thread emphasised this, when venturing to go to a dark sky location, if conditions are suitable, then we expect that it will be for a good few hours.

During those meaningful few hours, the cold and fatigue are ignored, anything else is dimmed, the thing that gains in relevance is what your telescope is capable of showing you in the dark transparent sky. As you will be aware, you simply become sensitive to looking over the passing hours and objects such as the Crescent will reveal themselves with certainty.

[25585]

1 hour ago, Littleguy80 said:

Agree. Excellent post @Louis D! I wonder if familiarity with the targets themselves is key too. I find, even with something like the moon, comparing the view through the eyepiece to an Atlas normally results in me seeing details that I otherwise would have missed

I think familiarity is key. And how a scope design presents a FOV eg south on top, guide stars etc.

Looking for stuff in a populated field of view takes grim determination. How do galaxy spotters manage looking into galaxy clusters etc?

Anyway, gradually narrowing down FOV using smaller focal length eye pieces, or a zoom, is to me the best way I have found. Every scope from F10 to F5 I have, has a 20 to 25mm ep in its kit, whether for low, mid or higher magnification.

 

[scarp15]

2 hours ago, jetstream said:

I totally agree Stu and this is why I go to an object repeatedly over the course of an evening to get the object recognition going. I pick objects to go over- and- every session until they get into the memory or whatever, the Little Veil is a prime example as is the Jellyfish (and many more). Now these objects show much easier and with more detail.

The Little Veil is a prime example of an exacting object to visually grasp. Upon determining a possible observed account (which equally is good to share the account with others to exchange / compare references), you then formulate, store the star pattern and (suggestive / vague) profile within your minds eye. To then go back and attempt to verify (true or false) or build on your observation, familiarity and awareness of extent of difficulty, enables a bit more clarity (or at least confirmation) to visually come through. At least that's what I hope for when I have another go at the Little Veil late Summer - and using my span of 20-25mm eyepieces (coupled to an OIII filter) for the task, their glass element composition, so much as their exit pupil being of relevance.  

[John]

I agree that Louis D's post is an excellent summary of techniques that can be developed with practice and do make a difference.

When I've had an intense deep sky session (which I've not done for quite a while I have to admit ) I've found that after a couple of hours with no surrounding lighting, no illuminated handset or tablet, my mind and eye and to some extent the rest of me gets what I call "into the groove" and I find that I can move from target to target across the sky with more ease, almost feeling connected to both the sky and the scope. It sounds a bit silly to describe it that way but thats the way that my best deep sky sessions have felt

It's actually a very rewarding experience when it all comes together. What it's all about, really.

 

[Paz]

15 hours ago, Littleguy80 said:

I’ve often wondered what makes the difference with an experienced observer. What’s visible in the eyepiece must be the same so what does the experience teach you that allows you to see more? 

LouisD has provided a great answer to this. Ive had an interesting experience for observing variable stars recently. As it involves really concentrating on certain stars for some time Ive started to be able to pick out fainter stars because Ive somehow subconsciously learned more about how to pick them out, and oddly from this type of observing I now notice more subtle star colours when colour never really used to register with me unless it was really obvious. Im not sure how this last development works but there you go.