Im Stuck

[Paul2019]

Recently I bought a new lens for my 400D, its a tamron 70-300mm. I finally had a chance to try it out last night and I could achieve focus @ 70mm, this was at the infinity mark. If i add anymore length to the lens (i.e 135mm +) i couldnt acheive focus. Any ideas what im doing wrong? 

 

Thanks in advance for any help 

 

[Cornelius Varley]

28 minutes ago, Paul2019 said:

Recently I bought a new lens for my 400D, its a tamron 70-300mm. I finally had a chance to try it out last night and I could achieve focus @ 70mm, this was at the infinity mark. If i add anymore length to the lens (i.e 135mm +) i couldnt acheive focus. Any ideas what im doing wrong? 

 

Thanks in advance for any help 

 

Are you trying to focus manually or automatic ? Does the lens work in daylight ?

[Paul2019]

2 hours ago, Cornelius Varley said:

Are you trying to focus manually or automatic ? Does the lens work in daylight ?

Using manual focus, works fine in daylight. When I up the FL it feels like it needs to go past infinity, The stars are very very bloated and clearly out of focus. But at the lowest FL its fine? Is it a dodgy lens or am I screwing it up somehow?

[Wyvern]

Hi,

I'm by no means an expert on telephoto's and how they should work, but what I will say is that when running my Canon 1100d and 100d models, is that star focus is always acheived before reaching the infinity mark on every lens I've used, and that's for both Canon brand and other manufacturers lenses in my kit.

Kinda leaning towards "faulty" lens if you're still trying to get to focus at the infnity stop with 135mm and higher.

Sorry,

Les

[Shimrod]

3 hours ago, Paul2019 said:

Using manual focus, works fine in daylight. When I up the FL it feels like it needs to go past infinity, The stars are very very bloated and clearly out of focus. But at the lowest FL its fine? Is it a dodgy lens or am I screwing it up somehow?

Are you sure it is definitely out of focus? A couple of thoughts:

1) You could be experiencing zoom creep - if you have the lens pointing upwards, on a long exposure the zoom can slowly move backwards. You could check this (in the daytime) by pointing the camera upwards, take a short exposure at a long focal length, wait (however many seconds you are exposing for) and take another shot. See what focal length is recorded in the EXIF data for the two photographs. If they are different, then you need to find a way to stop the lens moving.

2) Do you have a stable tripod? You could be experiencing a bit of wobble in your images either by the wind catching the tripod, or mirror slap causing the camera to vibrate.  There is an option in the menu to lock the mirror before activating the shutter which will reduce vibration - if it is wind blowing against the camera/tripod you could try hanging some weight from the tripod to give extra stability.

 

[vlaiv]

Maybe try something like this:

https://richardhaw.com/2017/10/21/repair-infinity-focus-calibration-12/

 

[Paul2019]

2 hours ago, Shimrod said:

Are you sure it is definitely out of focus? A couple of thoughts:

1) You could be experiencing zoom creep - if you have the lens pointing upwards, on a long exposure the zoom can slowly move backwards. You could check this (in the daytime) by pointing the camera upwards, take a short exposure at a long focal length, wait (however many seconds you are exposing for) and take another shot. See what focal length is recorded in the EXIF data for the two photographs. If they are different, then you need to find a way to stop the lens moving.

2) Do you have a stable tripod? You could be experiencing a bit of wobble in your images either by the wind catching the tripod, or mirror slap causing the camera to vibrate.  There is an option in the menu to lock the mirror before activating the shutter which will reduce vibration - if it is wind blowing against the camera/tripod you could try hanging some weight from the tripod to give extra stability.

 

I don't think it's zoom creep or the mirror but it's possible I guess, I'm using a hefty mafrotto tripod. I did have another play with it in daylight and seems that to achieve focus on a distant (2 miles away) object that I have to hit infinity and twerk it back just a fraction, something I didn't try last night. So possibly me just being daft in actually getting focus. If it clears tonight I'll get some images to show what's happening 

2 hours ago, vlaiv said:

Maybe try something like this:

https://richardhaw.com/2017/10/21/repair-infinity-focus-calibration-12/

 

Great link, thanks! 

[Paul2019]

6 hours ago, Paul2019 said:

Using manual focus, works fine in daylight. When I up the FL it feels like it needs to go past infinity, The stars are very very bloated and clearly out of focus. But at the lowest FL its fine? Is it a dodgy lens or am I screwing it up somehow?

I missed this one, I think you may be right, but testing this evening will determine this I reckon. Pictures to follow later on 

[Paul2019]

Turns out it was just me being thick, heres a very roughly processed M31 i took tonight @300mm FL

 

[rickwayne]

Well, that's all right then!

The infinity stop is usually worthless on modern autofocus lenses -- why bother making it accurate when the punters will never use it?

If you're not already using live view, a magnifier, and a Bahtinov mask, those are three good ways to ease achieving good focus. But maybe you already knew that.

[Shimrod]

5 hours ago, rickwayne said:

Well, that's all right then!

The infinity stop is usually worthless on modern autofocus lenses -- why bother making it accurate when the punters will never use it?

If you're not already using live view, a magnifier, and a Bahtinov mask, those are three good ways to ease achieving good focus. But maybe you already knew that.

I sturggle getting focus when using my camera & lens for astro work. It's much easier to connect a table and use a 7" or 10" screen to check the image.

@Paul2019 would you mind sharing what the problem was - it may help someone else in the future?

[Crackabarrel]

I have this same lens for my Nikon, it gets quite soft I found past about 130mm FL which could be part of the reason you see it as out of focus.