New TAKAHASHI DZ arrived

[John]

What about that old "meaningless magnification" thing that used to get quoted a lot when referring to scope performance ?

How do these top quality refractors seem to bypass that ?

 

[John]

5 minutes ago, John said:

What about that old "meaningless magnification" thing that used to get quoted a lot when referring to scope performance ?

How do these top quality refractors seem to bypass that ?

 

Actually, maybe a subject that is better discussed in a thread of it's own perhaps.

 

[mikeDnight]

1 hour ago, John said:

Actually, maybe a subject that is better discussed in a thread of it's own perhaps.

 

You're probably right John.  In the user manual to the DZ,  Tak do say that 200X is the limit for this aperture. But then they go on to say that the DZ is a high power instrument that will go well beyond the generally accepted 200X when the seeing conditions allow. They steer clear of stating a high power limit. I remember my old FS128 user manual claimed 100X to 120X per inch on a good night. I suspect they got some flack from some owners when their local seeing wouldn't allow that power to be used. I once used mine at 800X while observing Uranus. It was empty magnification of course, but the image did remain nice and sharp. I think it must be magic!

[andrew s]

Pending a new thread. Taking the definition of empty magnification as making the image scale such that the images highest resolution components are over sampled by the eye (I.e. the eye could fully resolve it at a lower magnification) then if the illumination is high enough and the atmosphere steady enough then there should be no issue.

The number was set in an era of lower quality optics, especially eyepiece design, by heuristics based on observation. As with the various resolution limits they are arbitrary. 

Science does not provide hard and fast numbers only useful ones in specific cases.

Regards Andrew 

Edited April 30, 2020 by andrew s

[F15Rules]

3 hours ago, mikeDnight said:

You're probably right John.  In the user manual to the DZ,  Tak do say that 200X is the limit for this aperture. But then they go on to say that the DZ is a high power instrument that will go well beyond the generally accepted 200X when the seeing conditions allow. They steer clear of stating a high power limit. I remember my old FS128 user manual claimed 100X to 120X per inch on a good night. I suspect they got some flack from some owners when their local seeing wouldn't allow that power to be used. I once used mine at 800X while observing Uranus. It was empty magnification of course, but the image did remain nice and sharp. I think it must be magic!

The images below are from the user manual of my FS128.. they clearly advise that, given optimum sky conditions, the FS series (all of them, not just the larger apertures) can take up to x120 per inch of aperture, and up to x100 per inch on planetary observing.

I can't vouch for these figures myself, as a) my eyepieces won't go above about x335 (which is x67 per inch in my scope), and b) I haven't had any optimum planetary observing opportunities since I bought the scope!

From previous planetary observing sessions with an excellent 5" F15 D&G achromat and Vixen ED103s F7.7 Apo, I think it would depend on the individual planet as much as the sky conditions. For example, at the last really good Mars opposition I was able to ramp up the magnification significantly (and the same for Saturn): but on Jupiter I have never been able to go much above about x240-250 without feeling I lost more sharpness at higher powers than I gained in detail?

I'm absolutely sure, though, that all Tak 4" apos will take at least x75 per inch of aperture routinely, on most objects. I'm also sure that someone like Mike has eyes, which work so much better than mine, which very likely could go up to x100 or more per inch on the best nights😀

Dave

Edited April 30, 2020 by F15Rules

[John]

I don't think I've read the manual that came with my Tak

I'll have to dig it out and have a look though it - might pick up some useful tips !

[BGazing]

Congrats! 

If I understand correctly, the dew shield is 'shallower' than that on the DC and DF? I used dew shield on my Tak only in extremely dewy conditions, normal usage does not require it.

 

[mikeDnight]

2 hours ago, John said:

I don't think I've read the manual that came with my Tak

I'll have to dig it out and have a look though it - might pick up some useful tips !

Its a guy thing!  Instruction manuals are usually only of any use when all else fails. When i was younger i spent three days building a sliding door fitted wardrobe, and at the end of it I finished up with an MFI bedroom shed; proving that sometimes its best to ignor instructions. But as regards your DL, you may find out you've been looking through the wrong end all this time John! 

[mikeDnight]

1 hour ago, BGazing said:

Congrats! 

If I understand correctly, the dew shield is 'shallower' than that on the DC and DF? I used dew shield on my Tak only in extremely dewy conditions, normal usage does not require it.

 

Im not sure. I know my DC dewshield didn't extend far beyond the front of the lens cell. The FC's lens cell is quite chunky and occupies a significant amount of the dew shield. I'd imaging the DC and DF  are the same. The DZ shield extends 80mm beyond the front edge of the lens cell despite the shade looking quite long.

This was my FC100DC dew shield showing how much the room cell occupies. It's probably the same as the DZ.

[John]

That looks similar to my DL. I've not had any dewing issues, so far, with that scope though.

 

[paulastro]

Andrew s said:

Pending a new thread. Taking the definition of empty magnification as making the image scale such that the images highest resolution components are over sampled by the eye (I.e. the eye could fully resolve it at a lower magnification) then if the illumination is high enough and the atmosphere steady enough then there should be no issue.

Andrew.  Regarding the illumination being high enough, this is what I think of  myself as meaning 'empty magnification' .     I have discussed this issue with Mike several times.  I'm sure Mikes DZ will, on nights of excellent seeing, be capable of 'taking' magnification even higher than the x500 Mike has already used on Venus with this scope.  For me at least, even with the superb optics of the DZ, at x500 power on a planet, with my aging eyesight the image would be too dim for me to pick out some  features which I may pick up at x250 or so with no problem.  This is why, my preference is for a SW 120ED to any of the FC 100mm refractors, the 120 providing me the opportunity to work with higher magnifications than I could with the 100 mm scope.  In passing, the theoretical better resolution of the 120 is of no account, as I don't often get sub-arc second seeing unfortunately at home.  Also the superior quality of the Tak optics would probably beat the practical resolution of the SW optic when the seeing is particularly good anyway.

I'd be interested to hear what others think about this.

[BGazing]

7 hours ago, paulastro said:

Andrew s said:

Pending a new thread. Taking the definition of empty magnification as making the image scale such that the images highest resolution components are over sampled by the eye (I.e. the eye could fully resolve it at a lower magnification) then if the illumination is high enough and the atmosphere steady enough then there should be no issue.

Andrew.  Regarding the illumination being high enough, this is what I think of  myself as meaning 'empty magnification' .     I have discussed this issue with Mike several times.  I'm sure Mikes DZ will, on nights of excellent seeing, be capable of 'taking' magnification even higher than the x500 Mike has already used on Venus with this scope.  For me at least, even with the superb optics of the DZ, at x500 power on a planet, with my aging eyesight the image would be too dim for me to pick out some  features which I may pick up at x250 or so with no problem.  This is why, my preference is for a SW 120ED to any of the FC 100mm refractors, the 120 providing me the opportunity to work with higher magnifications than I could with the 100 mm scope.  In passing, the theoretical better resolution of the 120 is of no account, as I don't often get sub-arc second seeing unfortunately at home.  Also the superior quality of the Tak optics would probably beat the practical resolution of the SW optic when the seeing is particularly good anyway.

I'd be interested to hear what others think about this.

My DF mags are as follows:

Moon in good seeing - 185x, if superb 212x, if iffy, 150.

Jupiter 150x, Saturn 150-185x. Mars 185-212x. Venus what the seeing allows but not more than 212x.

260x on Moon if seeing is stupendous. I have not tried 250x on Mars, did not have the EP at the time.

At 185x my floater population is still not intrusive. At 212x it is borderline acceptable. 

Except for the Moon and Mars, other Solar system targets get dim for me with additional magnification. Moon can take it but then the floaters kick in.

My 'good' seeing caps at around 200x, so it is not I am missing much normally. My more common 'not great not terrible' seeing is around 150x.

[John]

I find with my Tak FC-100DL that I'm starting at around 200x and going upwards on all the above except Jupiter which just does not seem to benefit from much above 200x mostly. I did not think that my Nagler 2mm - 4mm zoom would get so much use !

 

[BGazing]

I tried 212x (that's 3.5mm) on Jupiter only once when the seeing was superb, and then only to enlarge some details at the expense of losing color. It was not bad but the view became almost monochrome. Below 0.7 exit pupil Jupiter quickly becomes bland. Mars, on the other hand...

[paulastro]

7 hours ago, BGazing said:

My DF mags are as follows:

Moon in good seeing - 185x, if superb 212x, if iffy, 150.

Jupiter 150x, Saturn 150-185x. Mars 185-212x. Venus what the seeing allows but not more than 212x.

260x on Moon if seeing is stupendous. I have not tried 250x on Mars, did not have the EP at the time.

At 185x my floater population is still not intrusive. At 212x it is borderline acceptable. 

Except for the Moon and Mars, other Solar system targets get dim for me with additional magnification. Moon can take it but then the floaters kick in.

My 'good' seeing caps at around 200x, so it is not I am missing much normally. My more common 'not great not terrible' seeing is around 150x.

Many thanks Andrew.  I tend to be on the higher side of yourself Andrew with the 120ED,  on Mars at opposition I would use 300x plus depending on seeing.  I do use a binoviewer though which is much better than single eye pieces, at least for me anyway..  I find using a binoviewer also just about eliminates floaters under most circumstances

[paulastro]

5 hours ago, John said:

I find with my Tak FC-100DL that I'm starting at around 200x and going upwards on all the above except Jupiter which just does not seem to benefit from much above 200x mostly. I did not think that my Nagler 2mm - 4mm zoom would get so much use !

 

Thanks John.  I've always found Taks capable of gobbling up magnification too, and the DL I had was no exception.  I also find that I can rarely gain anything by using more than x200 on Jupitet, even with my binoviewer.  If I ever got to the giddy heights of x300 I'd be very surprised.

[mikeDnight]

I find Jupiter, and Saturn too for that matter, to be at it's best between 170X and 200X.  Much beyond these powers the view becomes soft and the intricate belt or ring detail loses definition and contrast. In my mind this is due to the type of detail being observed. With Jupiter and Saturn, the detail being studied is not merely albedo differences, but very real, dynamic, ultra fine and intricate and colourful. Mars on the other hand is a mass of shades. Mars is also usually quite small and bright, so the higher mags not only enlarge the disc but also dim the view which can benefit the trained eye by allowing subtle differences to be detected. E. E.Barnard prefered 180X for his planetary observing even with a 40" frac. 

I find the Moon on the other hand to be plenty bright enough to allow high powers, even in small scopes, without the image becoming too dim or too soft, providing the seeing and the scope allows. And as regards floaters, I have them in abundance. Looking straight down into the eyepiece from above, they seem to settle right in front of the target I'm Looking at. Turning the diagonal to the side helps a little as the floaters drift across the field but tend not to block the view. Binoviewing the Moon and planets helps a great deal with both floaters and in reducing the effects of turbulence, so like paulastro, I'll try to use a binoviewer in preference to a single eyepice. Although lately I'm having a lot of fun using Vixen s high resolution eyepieces. 

Edited May 1, 2020 by mikeDnight

[John]

Some important points there Mike

I've also found that some eyepieces are better for, say Jupiter, than they are with, say Mars and vice versa.

Each planetary target has it's own specific characteristics and the approach needed to get the best out of them needs to be tailored accordingly.

 

[mikeDnight]

1 hour ago, John said:

Some important points there Mike

I've also found that some eyepieces are better for, say Jupiter, than they are with, say Mars and vice versa.

Each planetary target has it's own specific characteristics and the approach needed to get the best out of them needs to be tailored accordingly.

 

I agree completely!  A few years ago i was reading about how different eyepieces can be used to enhance certain planetary detail. It was claimed, probably quite rightly, that Televue plossl's were good for observing Jupiter because of their warm tone. Where as RKE's were better for Saturn because of their cool clarity. The draw back of course is that it can become very expensive, not to mention cumbersome, if we need to carry around case loads of specific designs for specific uses. I'm not sure my owner will approve!

[BGazing]

4 hours ago, paulastro said:

Many thanks Andrew.  I tend to be on the higher side of yourself Andrew with the 120ED,  on Mars at opposition I would use 300x plus depending on seeing.  I do use a binoviewer though which is much better than single eye pieces, at least for me anyway..  I find using a binoviewer also just about eliminates floaters under most circumstances

Andrew?

[paulastro]

Oops, sorry.

[Sunshine]

On 27/04/2020 at 06:53, mikeDnight said:

I've been in a no-mans-land since the DC left me, and have even resorted at times to using one of those scopes with a mirror at the bottom end, - I forget what they're called! 

This had me laughing!

[JeremyS]

1 hour ago, Sunshine said:

This had me laughing!

Yes @mikeDnightoften has this effect on people. Key is to make him think we are laughing with him 🤣