Harpia 95 Depth Of Field At Full Zoom. (1 Viewer)

[Simmo1111]

Harpia 95 Focus Problem At Full Zoom.

I've had a Zeiss Harpia 95 for a few months now but am still struggling with the focus at full zoom. The focus adjustment seems to be so 'narrow' that when turning the focus ring, just as the image looks to be sharpening, a slight extra turn of the focus ring (all done very slowly) pushes it past the focus point and I start to lose the sharpness of the image again. I'm constantly hunting back and forth with the focus wheel to try and get a sharp image. At full zoom the scope is basically a waste of time. Not having tried another one for comparison I don't know if this is normal or whether my scope isn't functioning as it should. I've contacted Zeiss via email and still had no answer to my, what I thought was, a simple question. Does anyone else using a Harpia 95 have the same issue with their scope at full zoom? Sadly, at this point, I'm wishing I had bought a Swaro ATX instead.

This post has been edited as I originally asked about the 'depth of field' at full zoom but having read a few posts, it seems that depth of field isn't really the right way to describe it.


Thanks very much.

 

[henry link]

"Focus hunting" is a possible sign of excessive aberrations, typically spherical aberration or astigmatism. No scope brand or model is immune. You may have noticed the mention of "star-testing" as a way to diagnose the problem or problems that cause observations like yours. Id start with reading this thread.

https://www.birdforum.net/showthread.php?t=386338

 

[Simmo1111]

"Focus hunting" is a possible sign of excessive aberrations, typically spherical aberration or astigmatism. No scope brand or model is immune. You may have noticed the mention of "star-testing" as a way to diagnose the problem or problems that cause observations like yours. Id start with reading this thread.

https://www.birdforum.net/showthread.php?t=386338

Thanks very much Henry, I'll take a look.

 

[jring]

Hi,

both are actually a thing... as Henry stated, aberrations can make finding a clear point of best focus difficult at high magnifications - you have more of a wide range of least fuzziness, but no good focus. Star testing the scope can help to find out what aberrations are present.

On the other hand, the depth of focus with fast instruments and high magnifications can get very slim, so getting to best focus needs very delicate adjustments - ideally with a dual speed focus drive, which the Harpia claims to have, although not in the traditional sense with two knobs but with one barrel which should switch between two speeds.

If this doesn't work, I can imagine that leading to the symptom you describe.

Joachim

 

[Simmo1111]

Hi Joachim and thanks very much for your reply.

It seems that the slow focus is working OK but the actual point of focus at full zoom is so miniscule that it is very easy to miss it and go too far. Even on a static object I have this problem.
When I've paid over £3000 for a spotting scope it's extremely disappointing to find that it's more or less useless at 70x zoom. I bought it for seawatching among other things but trying to focus at 70x on a distant bird is a complete waste of time. It may be that this is 'normal' and I'm trying to do something which the scope cannot achieve but when the cost of the scope is so high and the reviews are so good you expect it to work well. If the scope is sold with a 70x zoom then it should work OK at that.

Thanks again for your help.

 

[jring]

Hi,

well, I'm not a big fan of barrel focus drives, so take what I say with a pinch of salt. My old Kowa TSN-3 has a single focus knob and with that I can focus well at 96x - if the seeing allows it (this is another point, depending on the temperature you can get into a situation where heat haze will make it impossible to get a clear image for more than a second at higher magnification - regardless of the qualitiy of the optics and the focus drive).

Joachim

 

[Simmo1111]

Thanks again Joachim,

I understand what you mean about atmospherics playing a big part. With that in mind I have tried the scope in the evening when the air is cooler but still have the same problem. A representative from Zeiss has been good enough to contact me to see if we are able to resolve the issue.

Dave.

 

[henry link]

To minimize the issue of unsteady air try using a resolution target at a relatively short distance, perhaps 10-30 meters, preferably over shaded grass.

Henry

 

[Simmo1111]

Thanks Henry,

I'm looking forward to testing my scope alongside the same model which a friend if mine uses. I haven't had the chance to do that yet but hopefully this itself will at least answer my question if there are obvious differences. I posted my original thread wondering if there were any more Harpia users out there who had the same problem as I do. Looking at Joachim's reply it sounds as though I should have bought a Kowa! Sharp at 96x zoom is a vast improvement on my struggle to focus at 70x

Dave.

 

[DRodrigues]

Thanks Henry,

I'm looking forward to testing my scope alongside the same model which a friend if mine uses. I haven't had the chance to do that yet but hopefully this itself will at least answer my question if there are obvious differences. I posted my original thread wondering if there were any more Harpia users out there who had the same problem as I do. Looking at Joachim's reply it sounds as though I should have bought a Kowa! Sharp at 96x zoom is a vast improvement on my struggle to focus at 70x

Dave.

Most probably a bad sample. The Harpia 95 I tried hadn't the problems you describe and was even sharper than my STX95 at the centre of the field http://www.pt-ducks.com/cr-telescopes.htm#Swarovski_X95_vs_Zeiss_Harpia95, but the Swaro is also sharp at 122x...
Comparing your sample to the one of your friend should show the differences - let us know what you will find.

 

[Simmo1111]

Thanks David,

I'll let you know what the outcome is.

 

[henry link]

One note of caution. The other scope really needs to be sensibly perfect for a useful comparison. It wouldn't be a big surprise if both scopes are suboptimal.

The advantage of a star test is that it compares your scope to an absolute optical standard, not another scope of unknown quality, and it also gives you a diagnosis of what's wrong if your scope has problems.

 

[Simmo1111]

Thanks Henry,

My friend has said that his Harpia is the best scope he's ever used so I'm hoping that when he tries mine that he will see some obvious differences between them. Zeiss have kindly offered to replace the scope with another one if there is a problem so we'll see what happens. A star test is definitely something I intend to do as well when I get the chance as this (if I get it right) will give me something to pass back to Zeiss with regard to my particular scope.

Thanks again.

 

[OhWeh]

In the first days/tries possessing the Harpia, I also thought, that the Harpia is not totally sharp at max. enlargement.

In my case, this was a problem with the (slight) wobbling air, with "seeing".

The Harpia is (my subjective impression) so sharp and with best contrast, that you miss something immediately, if you don't get this quality, due to air problems.

I had to change acouple of times between Harpia95 and ATX95 (we have both models) to understand this. The sight through the ATX was as bad as through the Harpia (due to the air), but the ATX is not as brilliant as the Harpia, so you don't miss the "optimum" so fast.

I hope you can imagine what I want to say.

 

[Simmo1111]

Thanks very much OhWeh,

I understand what you mean about the air temperature and have seen this through my scope. I did also wonder if it could be 'wobble' from my tripod which is preventing a sharp image. That said, I have used the scope in a hide with the tripod set very low so it was very stable but I still struggled to focus at 70x zoom. I would be interested to try an ATX alongside my Harpia so will ask around and see if anyone near to me has one which I could try out.

 

[Simmo1111]

I tried a star test last night just as a 'tester' to see if I could do it properly. First one I've ever done so I don't know whether the results were of any use or not.

The star looked to be a uniformly shaped slightly fuzzy disc when I got to what appeared to be the best focus point. As I pushed the focus past this point, the image turned into something resembling a sort of knobbly pollen grain which appeared to have a fireball sort of appearance. No rings visible, just a flaming ball. On pulling the focus back to a spot before the actual focus point, the image was of uniformly shaped concentric rings but the outer ring looked as though it was on fire, a bit like the flaming hoops you see in circuses etc.

That's about the best I can do for a description.

Does that mean anything to you guys who have carried these tests out or should I have another go and be looking for anything in particular?

Thanks very much.

 

[henry link]

Hi Dave,

Any motion you see is air turbulence, which unfortunately obscures the patterns you want to see. Choosing a star close to the zenith and avoiding warm ground surfaces in front of the scope might help, but sometimes there is a layer of turbulence in the atmosphere that can't be eliminated. That's one reason I usually use an artificial star set up over a grassy lawn in daylight or sometimes an indoor set-up.

That said, strong rings on one side of focus and no rings on the other side is a bad sign. If that persists in calm air it would indicate high spherical aberration, which is one of the defects that leads to "focus hunting" at high magnification.

Henry

 

[Simmo1111]

Thanks Henry,

I'll have a few tries in different conditions and see if the results are constant. I'll let you know.

Thanks again.

PS. I did the test at 00:30 just in case that might discount any air turbulence. I used the pole star.

 

[jring]

Hi,

so far it looks like it's undercorrected to some degree - the question is how much. But no rings at all beyond focus and very strong outer ring before is indeed a bad sign.

Here's some examples - look for Balanced spherical primary images in the unobstructed case. Shown are lambda/4 or quarter wave (which is diffraction limited for primary SA and the accepted lower boundary for an "ok" scope) and lambda/8 (which is fairly good).

https://www.telescope-optics.net/star_testing_telescope.htm

As for Polaris, that should be high enough ;-) Try observe on grass, not hot concrete ot tarmac.

Joachim

 

[Simmo1111]

Just to add to the mix. I had another play with the focusing on the Harpia and have noticed this:

When focusing on 70x zoom, I turn the focus wheel very slowly when approaching the point of sharpness and, just as the image is starting to focus, it starts to blur again as usual. Let's say (for the sake of this observation) that I've turned the focus wheel 3mm too far. I would expect that if I turn the focus wheel back by the 3mm I should be somewhere near to the missed focus point. This is not the case though. I have to turn the wheel much further than the expected 3mm. It might be more like 30mm, possibly even more, before the image begins to sharpen again. This appears to be adding to the problem of my having to 'focus hunt' in order to try to find the sweet spot. It all seems to go against what your brain would expect to be logical with regard to the mechanics of the focus arrangement. It's almost as though there is far too much play in between altering the focus in one direction and then going back in the other direction. In my engineering days it would be akin to excessive 'backlash' when we were working with gears and gearboxes etc.

Do any of you Harpia owners have the same thing with yours? It may be that this is how the focusing mechanics of the Harpia are but if so, it's very wierd and very difficult to get used to.

Thanks.